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_base.cpp

@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "command_base.h"
+#include "core/qthelper.h" // for updateWindowTitle()
+#include "core/subsurface-qt/DiveListNotifier.h"
+
+namespace Command {
+
+static QUndoStack undoStack;
+
+// General commands
+void init()
+{
+	QObject::connect(&undoStack, &QUndoStack::cleanChanged, &updateWindowTitle);
+}
+
+void clear()
+{
+	undoStack.clear();
+}
+
+void setClean()
+{
+	undoStack.setClean();
+}
+
+bool isClean()
+{
+	return undoStack.isClean();
+}
+
+QAction *undoAction(QObject *parent)
+{
+	return undoStack.createUndoAction(parent, QCoreApplication::translate("Command", "&Undo"));
+}
+
+QAction *redoAction(QObject *parent)
+{
+	return undoStack.createRedoAction(parent, QCoreApplication::translate("Command", "&Redo"));
+}
+
+bool execute(Base *cmd)
+{
+	if (cmd->workToBeDone()) {
+		undoStack.push(cmd);
+		emit diveListNotifier.commandExecuted();
+		return true;
+	} else {
+		delete cmd;
+		return false;
+	}
+}
+
+} // namespace Command
+
+