Add a material list lookup for the element article fields

The element description dialog only offered typing, so every article of
a catalogue had to be copied in by hand into the Artikelbeschreibung
row of each block, over and over.

Settings > General now keeps the path of a CSV material list (Créer...
writes a template with the header lines), and the Artikelbeschreibung
row of every block of the Bauteil dialog shows a "..." button opening a
searchable listing of that file. "Appliquer" fills the fields of that
block only -- the main block gets everything but label and formula, an
auxiliary block gets description, number, manufacturer, references,
supplier, quantity, unit and additional info -- and a cell that is
empty in the file never erases a value already in the element. The
symbol editor is left alone.

- sources/materiallist/: CSV reading and writing (UTF-8 BOM, ';', every
  field quoted, atomic write through QSaveFile), two header lines
  (translated labels then the canonical English keys), the selection
  window and the new entry form.
- The selection window reads the file again every time it opens, keeps
  its size, column widths, column order and sort between openings,
  shows every column of the file, scrolls all four directions with the
  wheel (Shift + wheel moves the columns) and puts back the order of
  the file when the corner above the row numbers or a row number is
  clicked.
- German translations for the new strings in lang/qet_de.ts.

sources/ui/elementinfowidget.cpp

@@ -20,8 +20,11 @@
 #include <QCheckBox>
 #include <QPushButton>
 #include "../diagram.h"
+#include "../materiallist/materiallist.h"
+#include "../materiallist/materialselectiondialog.h"
 #include "../qetapp.h"
 #include "../qetgraphicsitem/element.h"
+#include "../qetmessagebox.h"
 #include "../dataBase/projectdatabase.h"
 #include "../qetinformation.h"
 #include "../qetproject.h"
@@ -222,6 +225,8 @@ void ElementInfoWidget::buildInterface()
 		m_eipw_list << eipw;
 	}
 
+	setupMaterialButtons();
+
 	m_add_custom_property_btn = new QPushButton(tr("Ajouter une propriété personnalisée"), this);
 	connect(m_add_custom_property_btn, &QPushButton::clicked, this, [this]() { addCustomProperty(); });
 	ui->scroll_vlayout->addWidget(m_add_custom_property_btn);
@@ -332,6 +337,150 @@ ElementInfoPartWidget *ElementInfoWidget::infoPartWidgetForKey(const QString &ke
 	return nullptr;
 }
 
+/**
+	@brief ElementInfoWidget::setupMaterialButtons
+	Show the "..." button opening the material file on the description row
+	of each block: one for the main article, one per auxiliary article
+	which really has a description row.
+
+	Only that row carries the button: the same window fills the whole
+	block, so repeating it on every field of the block would just offer
+	five ways to do the same thing.
+*/
+void ElementInfoWidget::setupMaterialButtons()
+{
+	auto register_button = [this](ElementInfoPartWidget *eipw, int block)
+	{
+		eipw->setMaterialButtonVisible(true);
+		connect(eipw, &ElementInfoPartWidget::materialButtonClicked, this,
+				[this, block]() { materialFromFile(block); });
+	};
+
+		//Main article. A terminal has no description row: its article
+		//number is the one which identifies it, so the button sits there.
+	if (ElementInfoPartWidget *eipw = infoPartWidgetForKey(QETInformation::ELMT_DESCRIPTION)) {
+		register_button(eipw, 0);
+	} else if (ElementInfoPartWidget *eipw = infoPartWidgetForKey(QETInformation::ELMT_DESIGNATION)) {
+		register_button(eipw, 0);
+	}
+
+		//Auxiliary articles 1 to 4.
+	const QStringList auxiliary_keys = {
+		QETInformation::ELMT_DESCRIPTION_AUX1,
+		QETInformation::ELMT_DESCRIPTION_AUX2,
+		QETInformation::ELMT_DESCRIPTION_AUX3,
+		QETInformation::ELMT_DESCRIPTION_AUX4
+	};
+
+	for (int block = 1; block <= 4 && block <= auxiliary_keys.size(); ++block)
+	{
+		if (ElementInfoPartWidget *eipw = infoPartWidgetForKey(auxiliary_keys.at(block - 1))) {
+			register_button(eipw, block);
+		}
+	}
+}
+
+/**
+	@brief ElementInfoWidget::materialFromFile
+	Open the material file, let the user pick an article, and write it
+	into the block the button belongs to.
+	@param block 0 for the main article, 1 to 4 for an auxiliary article
+*/
+void ElementInfoWidget::materialFromFile(int block)
+{
+		//Nothing configured yet: the standard location is used, the same
+		//one the preferences offer to create, so that the catalogue can be
+		//reached from here without asking for a file to be saved first.
+	QString path = MaterialList::configuredPath();
+	if (path.isEmpty())
+	{
+		path = MaterialList::defaultPath();
+		MaterialList::setConfiguredPath(path);
+	}
+
+		//A missing or empty file has no entry to pick: offer to write the
+		//header line instead of opening an empty window.
+	if (MaterialList::isEmptyFile(path))
+	{
+		const auto answer = QET::QetMessageBox::question(
+			this,
+			tr("Liste de matériaux absente"),
+			tr("Aucun fichier de liste de matériaux n'existe à cet emplacement :\n"
+			   "%1\n\nLe créer ?", "message asking to create the material file").arg(path),
+			QMessageBox::Yes | QMessageBox::No,
+			QMessageBox::Yes);
+
+		if (answer != QMessageBox::Yes) {
+			return;
+		}
+
+		QString error;
+		if (!MaterialList::createFile(path, &error))
+		{
+			QET::QetMessageBox::critical(this,
+										 tr("Création impossible"),
+										 tr("Impossible de créer le fichier :\n%1\n%2")
+											.arg(path, error));
+			return;
+		}
+	}
+
+		//The catalogue opens on the whole list : the search field starts
+		//empty, whatever the block already holds.
+	MaterialSelectionDialog dialog(path, this);
+	if (dialog.exec() == QDialog::Accepted) {
+		applyMaterialRecord(dialog.selectedRecord(), block);
+	}
+}
+
+/**
+	@brief ElementInfoWidget::applyMaterialRecord
+	Write a catalogue entry into the fields of one block.
+
+	Only the fields of that block are touched: applied to an auxiliary
+	article, the entry never reaches the main article. And a cell which is
+	empty in the file leaves the current value alone, so picking an entry
+	describing only the order reference never wipes a comment.
+	@param record the entry taken from the material file
+	@param block 0 for the main article, 1 to 4 for an auxiliary article
+*/
+void ElementInfoWidget::applyMaterialRecord(const MaterialRecord &record, int block)
+{
+	if (record.values.isEmpty()) {
+		return;
+	}
+
+		//Fill the fields without letting the live edit push one undo
+		//command per line edit: the whole entry must be undoable at once.
+	const bool live_edit = m_live_edit;
+	if (live_edit) {
+		disableLiveEdit();
+	}
+
+	for (const QString &column : MaterialList::columnsForBlock(block))
+	{
+		const QString value = record.value(column);
+		if (value.isEmpty()) {
+			continue;
+		}
+
+		const QString key = MaterialList::elementInfoKey(column, block);
+		if (key.isEmpty() || !QETInformation::elementInfoKeys().contains(key)) {
+			continue;
+		}
+
+		if (ElementInfoPartWidget *eipw = infoPartWidgetForKey(key)) {
+			eipw->setText(value);
+		}
+	}
+
+	if (live_edit) {
+		enableLiveEdit();
+	}
+
+	apply();
+}
+
 /**
 	@brief ElementInfoWidget::updateSuggestions
 	Offer, for each information, the values already used by the other