Refactoring: move undo commands to top level

In the future we might want to use undo-commands for mobile as
well (even if not implementing undo).

Therefore, move the undo-command source from desktop-widgets
to their own commands top-level folder.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

commands/command_edit_trip.cpp

@@ -0,0 +1,83 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "command_edit_trip.h"
+#include "command_private.h"
+#include "core/qthelper.h"
+
+namespace Command {
+
+EditTripBase::EditTripBase(dive_trip *tripIn, const QString &newValue) : trip(tripIn),
+	value(newValue)
+{
+}
+
+// Note: Virtual functions cannot be called in the constructor.
+// Therefore, setting of the title is done here.
+bool EditTripBase::workToBeDone()
+{
+	setText(tr("Edit %1").arg(fieldName()));
+	return data(trip) != value;
+}
+
+void EditTripBase::undo()
+{
+	QString old = data(trip);
+	set(trip, value);
+	value = old;
+
+	emit diveListNotifier.tripChanged(trip, fieldId());
+}
+
+// Undo and redo do the same as just the stored value is exchanged
+void EditTripBase::redo()
+{
+	undo();
+}
+
+// Implementation of virtual functions
+
+// ***** Location *****
+void EditTripLocation::set(dive_trip *t, const QString &s) const
+{
+	free(t->location);
+	t->location = copy_qstring(s);
+}
+
+QString EditTripLocation::data(dive_trip *t) const
+{
+	return QString(t->location);
+}
+
+QString EditTripLocation::fieldName() const
+{
+	return tr("trip location");
+}
+
+TripField EditTripLocation::fieldId() const
+{
+	return TripField::LOCATION;
+}
+
+// ***** Notes *****
+void EditTripNotes::set(dive_trip *t, const QString &s) const
+{
+	free(t->notes);
+	t->notes = copy_qstring(s);
+}
+
+QString EditTripNotes::data(dive_trip *t) const
+{
+	return QString(t->notes);
+}
+
+QString EditTripNotes::fieldName() const
+{
+	return tr("trip notes");
+}
+
+TripField EditTripNotes::fieldId() const
+{
+	return TripField::NOTES;
+}
+
+} // namespace Command