app: exit QtCoreApplication and dispose of systray icons on quit

Change-Id: I1a6e823121cf3268049c123e07653da4e424eec9

main.cpp

@@ -188,6 +188,12 @@ main(int argc, char *argv[])
         delete sem;
     });
 #endif
-
-    return a.exec();
+
+    auto ret = a.exec();
+
+    QCoreApplication::exit();
+    GlobalSystemTray::instance().deleteLater();
+    GlobalSystemTray::instance().hide();
+
+    return ret;
 }