Refactor window handling code

Currently when we want to show/raise the window in reaction to the tray icon/notification being clicked etc we do this by emitting a signal on the controller.
This is connected to in main.qml, which does some things, then calls back to controller to do more things.

This is quite convoluted. Instead introduce a new class WindowController that is responsible for all things window, in particular showing/raising and config saving

src/windowcontroller.cpp

@@ -0,0 +1,55 @@
+// SPDX-FileCopyrightText: 2022 Nicolas Fella <nicolas.fella@gmx.de>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "windowcontroller.h"
+
+#include <KConfig>
+#include <KWindowConfig>
+
+#ifdef HAVE_WINDOWSYSTEM
+#include <KWindowSystem>
+#endif
+
+#include <QStandardPaths>
+
+WindowController &WindowController::instance()
+{
+    static WindowController instance;
+    return instance;
+}
+
+void WindowController::setWindow(QWindow *window)
+{
+    m_window = window;
+}
+
+void WindowController::restoreGeometry()
+{
+    KConfig dataResource("data", KConfig::SimpleConfig, QStandardPaths::AppDataLocation);
+    KConfigGroup windowGroup(&dataResource, "Window");
+    KWindowConfig::restoreWindowSize(m_window, windowGroup);
+    KWindowConfig::restoreWindowPosition(m_window, windowGroup);
+}
+
+void WindowController::saveGeometry()
+{
+    KConfig dataResource("data", KConfig::SimpleConfig, QStandardPaths::AppDataLocation);
+    KConfigGroup windowGroup(&dataResource, "Window");
+    KWindowConfig::saveWindowPosition(m_window, windowGroup);
+    KWindowConfig::saveWindowSize(m_window, windowGroup);
+}
+
+void WindowController::showAndRaiseWindow(const QString &xdgActivationToken)
+{
+    if (!m_window->isVisible()) {
+        m_window->show();
+    }
+
+#ifdef HAVE_WINDOWSYSTEM
+    if (!xdgActivationToken.isEmpty()) {
+        KWindowSystem::setCurrentXdgActivationToken(xdgActivationToken);
+    }
+
+    KWindowSystem::activateWindow(m_window);
+#endif
+}