Don't start the entire NeoChat backend when receiving push notifications

This adds a dedicated "set up for push notifications only" function in
Controller, which only sets up the KUnifiedPush connector for receiving
the message and then quitting right afterward. If the user tries to
open a notification, then it will quit and open the main client.

src/controller.h

@@ -12,6 +12,10 @@
 #include <Quotient/jobs/basejob.h>
 #include <Quotient/settings.h>
 
+#ifdef HAVE_KUNIFIEDPUSH
+#include <kunifiedpush/connector.h>
+#endif
+
 class NeoChatRoom;
 class TrayIcon;
 class QQuickTextDocument;
@@ -119,6 +123,12 @@ public:
      */
     Q_INVOKABLE void forceRefreshTextDocument(QQuickTextDocument *textDocument, QQuickItem *item);
 
+    /**
+     * @brief Start listening for notifications in dbus-activated mode.
+     * These notifications will quit the application when closed.
+     */
+    static void listenForNotifications();
+
     Quotient::AccountRegistry &accounts();
 
 private: