Add a Target column to the terminal strip editor

Reading where a cable lands meant going back to the drawing: the strip
editor said which cable a terminal carries and which core, but never
what the cable goes to. A single core (1x16) could not be followed
from the terminal to its piece at all.

The new Target column names it: Installation, Location and Label (BMK)
of the piece the wires land on, past this strip, joined in one line --
the very three fields the strip drawing writes in the box under its
cable, in the same order (RealTerminal::cableTarget()). It is worked
out of the project like the Cable cells and so follows their rule: a
target the drawing names is read only, for only the drawing decides
it, and a cell nothing is worked out for takes an edit, so a target
the drawing cannot find -- a cable landing on a piece with no
Installation, Location nor Label set, a cable going to another strip
-- is still worth naming by hand. The text typed in is stored in the
element (RealTerminal::cableTargetInfoKey()) and kept until a cable
works a target out again, and back once that cable goes, exactly like
a cable designation typed by hand: the automatic value is never
written, so no stale text can be left behind. The column takes the
width of its own text, so a long Installation is never cut off.

A text typed in is written the way the fields are shown in the column,
"Installation / Location / Label", and gives one line per field: the
box under the cable draws three lines without any slash in them, just
like a target worked out from the project, instead of one long line
carrying its separators as text.

tst_terminalcableauto checks the column is empty -- and editable --
without a cable, reads "Plant 7 / Cabinet 7 / -S7" with one, goes
empty -- and editable again -- when the core is removed, takes no edit
while the drawing names the target, and is headed "Target"; a second
case checks a target typed in by hand is taken by the cell, stored by
Apply, shown again by a fresh model, set aside for the read only
target of the drawing once a cable lands somewhere worth naming, and
back once that cable goes; a third one the line per field. tst_cable
target paints a strip whose cable ends on one field and the same strip
ending on three, the second box two lines deeper than the first.

sources/TerminalStrip/ui/terminalstripeditor.cpp

@@ -249,6 +249,10 @@ void TerminalStripEditor::setCurrentStrip(TerminalStrip *strip_)
 		{
 			m_model = new TerminalStripModel{strip_, this};
 			ui->m_table_widget->setModel(m_model);
+				//The Target column is worked out from the drawing: it takes
+				//the width of its own text, never a cut off Installation
+			ui->m_table_widget->horizontalHeader()->setSectionResizeMode(
+				TerminalStripModel::CableTarget, QHeaderView::ResizeToContents);
 			m_model->buildBridgePixmap(setUpBridgeCellWidth());
 			connect(ui->m_table_widget->selectionModel(), &QItemSelectionModel::selectionChanged, this, &TerminalStripEditor::selectionChanged);
 		}
@@ -335,6 +339,12 @@ void TerminalStripEditor::apply()
 				if (!data_.cable_auto_) {
 					set_info(RealTerminal::cableInfoKey(), data_.cable_);
 					set_info(RealTerminal::cableWireInfoKey(), data_.cable_wire);
+				}
+					//The same for the target: a target worked out from the
+					//project is never written in the element, only the one
+					//typed in by hand is stored
+				if (!data_.cable_target_auto_) {
+					set_info(RealTerminal::cableTargetInfoKey(), data_.cable_target_);
 				}
 				set_info(RealTerminal::shieldInfoKey(), data_.shield_ ? QStringLiteral("true") : QString());
 				//The color and the section are stored with the dot as decimal separator, whatever the locale
@@ -790,7 +800,8 @@ void TerminalStripEditor::on_m_led_cb_activated(int index)
 namespace {
 /**
  * @return true if the cell at @a index contain a free text
- * (label, cable, wire of the cable, color, section or width), so a text can be pasted in it.
+ * (label, cable, wire of the cable, target of the cable, color, section
+ * or width), so a text can be pasted in it.
  */
 bool cellAcceptText(const QModelIndex &index)
 {
@@ -798,6 +809,7 @@ bool cellAcceptText(const QModelIndex &index)
 	return column_ == TerminalStripModel::Label
 			|| column_ == TerminalStripModel::Cable
 			|| column_ == TerminalStripModel::CableWire
+			|| column_ == TerminalStripModel::CableTarget
 			|| column_ == TerminalStripModel::Color
 			|| column_ == TerminalStripModel::Section
 			|| column_ == TerminalStripModel::Width;