Add saving and loading the configuration to a file (discussion #610)

Revives #640, closed only to clear a review backlog. Two entries in
the Configuration menu: "Enregistrer la configuration sous..." saves
the settings to a .conf file, "Charger une configuration..." replaces
them with one. The file is always ini format, so a profile made on one
platform loads on the others.

Changes from #640:
- Window sizes, positions and dock layouts (".../geometry",
  ".../state") and the recent-files lists stay out of a profile and
  are kept on load: they describe this computer, not a preference.
- A saved file carries a format marker; loading refuses files that
  QElectroTech did not save.
- Loading closes QElectroTech and asks the user to start it again,
  instead of starting a second copy: a second copy started while this
  one is still running hands its arguments over and exits (main.cpp).
- The colour dialog's custom colours are reloaded from the profile
  before quitting, since ~QETApp() saves them over the loaded ones.
- Both actions are registered with ShortcutManager, so they appear in
  command search and can be given a shortcut.
- The copy rules live in the header-only utils/configprofile.h and
  are unit tested (tst_configprofile).

Loading still replaces rather than merges: a setting the profile does
not have is removed, or switching profiles would keep settings from the
previous one.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

sources/qetapp.cpp

@@ -30,6 +30,7 @@
 #include "qetpalette.h"
 #include "qetstyle.h"
 #include "utils/qetutils.h"
+#include "utils/configprofile.h"
 #include "qetmessagebox.h"
 #include "qetproject.h"
 #include "qtextorientationspinboxwidget.h"
@@ -55,9 +56,11 @@
 #include <iostream>
 #define QUOTE(x) STRINGIFY(x)
 #define STRINGIFY(x) #x
+#include <QFileDialog>
 #include <QFontDatabase>
 #include <QProcessEnvironment>
 #include <QRegularExpression>
+#include <QSettings>
 #include <QStyleFactory>
 #include <QStyleHints>
 #ifdef BUILD_WITHOUT_KF
@@ -2242,6 +2245,109 @@ void QETApp::configureQET()
 #endif
 }
 
+/**
+	@brief QETApp::exportConfiguration
+	Save the settings of QElectroTech to a file the user chooses, to keep
+	them as a named profile or copy them to another computer (discussion
+	#610). The file is always written in the ini format, whatever the
+	platform stores its live settings in, so a profile saved on Windows
+	loads on Linux and macOS. See ConfigProfile for the keys left out.
+*/
+void QETApp::exportConfiguration()
+{
+	QWidget *parent_widget = qApp->activeWindow();
+
+	QString path = QFileDialog::getSaveFileName(
+				parent_widget,
+				tr("Enregistrer la configuration sous...", "dialog title"),
+				QString(),
+				tr("Configurations QElectroTech (*.conf)", "file dialog filter"));
+	if (path.isEmpty()) {
+		return;
+	}
+	if (!path.endsWith(QLatin1String(".conf"), Qt::CaseInsensitive)) {
+		path += QLatin1String(".conf");
+	}
+
+	QSettings live_settings;
+	QSettings file_settings(path, QSettings::IniFormat);
+	ConfigProfile::exportTo(live_settings, file_settings);
+
+	if (file_settings.status() != QSettings::NoError) {
+		QET::QetMessageBox::critical(
+					parent_widget,
+					tr("Erreur", "message box title"),
+					tr("Impossible d'enregistrer la configuration dans « %1 ».").arg(path));
+	}
+}
+
+/**
+	@brief QETApp::importConfiguration
+	Replace the settings of QElectroTech with a file saved by
+	exportConfiguration(), then close QElectroTech.
+
+	The settings are read by each part of QElectroTech when it starts, and
+	there is no signal telling all of them that a setting changed, so the
+	new settings are applied by starting QElectroTech again. That restart
+	is left to the user: a second copy started from here would find this
+	one still running, hand its arguments over to it and exit (main.cpp).
+*/
+void QETApp::importConfiguration()
+{
+	QWidget *parent_widget = qApp->activeWindow();
+
+	const QString path = QFileDialog::getOpenFileName(
+				parent_widget,
+				tr("Charger une configuration...", "dialog title"),
+				QString(),
+				tr("Configurations QElectroTech (*.conf)", "file dialog filter"));
+	if (path.isEmpty()) {
+		return;
+	}
+
+	QSettings file_settings(path, QSettings::IniFormat);
+	if (file_settings.status() != QSettings::NoError
+		|| !ConfigProfile::isProfile(file_settings))
+	{
+		QET::QetMessageBox::critical(
+					parent_widget,
+					tr("Erreur", "message box title"),
+					tr("« %1 » n'est pas une configuration enregistrée par QElectroTech.").arg(path));
+		return;
+	}
+
+		//Said before anything closes: once the last window is closed,
+		//QElectroTech quits by itself (checkRemainingWindows()).
+	const auto answer = QET::QetMessageBox::question(
+				parent_widget,
+				tr("Charger une configuration", "message box title"),
+				tr("Cette configuration va remplacer vos réglages actuels, sauf la "
+				   "disposition des fenêtres et la liste des fichiers récents.\n\n"
+				   "QElectroTech va ensuite se fermer. Relancez-le pour utiliser "
+				   "la nouvelle configuration.\n\n"
+				   "Voulez-vous continuer ?"),
+				QMessageBox::Yes | QMessageBox::No,
+				QMessageBox::No);
+	if (answer != QMessageBox::Yes) {
+		return;
+	}
+
+		//Asks to save any modified project, as quitQET() does. The settings
+		//are only replaced once every editor is closed, so that the editors
+		//saving their own settings on close cannot overwrite them, and a
+		//cancelled close leaves them untouched.
+	if (!closeEveryEditor()) {
+		return;
+	}
+
+	QSettings live_settings;
+	ConfigProfile::importFrom(file_settings, live_settings);
+		//~QETApp() saves the colour dialog's custom colours on exit: load
+		//the profile's into it first, or the old ones overwrite them
+	QET::loadCustomColors();
+	qApp->quit();
+}
+
 /**
 	@brief QETApp::aboutQET
 	Open the dialog about qet.