Fix wayland activation

Adds support for xdg_activation_v1 when calling the application from the
system tray by using KStatusNotifier which supports it.
Listens to XDG_ACTIVATION_TOKEN as it's passed when we are started from
dbus.

src/trayicon_sni.h

@@ -0,0 +1,19 @@
+// SPDX-FileCopyrightText: 2021 Aleix Pol Gonzalez <aleixpol@kde.org>
+// SPDX-License-Identifier: GPL-3.0-only
+
+#pragma once
+
+#include <KStatusNotifierItem>
+
+class TrayIcon : public KStatusNotifierItem
+{
+    Q_OBJECT
+public:
+    TrayIcon(QObject *parent = nullptr);
+
+    void show();
+    void hide();
+
+Q_SIGNALS:
+    void showWindow();
+};