Add CLI arguments parsing + --start-in-tray

- Loading a QML file in place of src/gui/UI.qml is now possible via
  -l / --load-qml instead of taking the first positional argument

- New option to start application in tray without showing a window

- --help and --version

src/main.cpp

@@ -186,7 +186,9 @@ int main(int argc, char *argv[]) {
     QQmlContext *objectContext = new QQmlContext(engine.rootContext());
 
     // To able to use Qt.quit() from QML side
-    QObject::connect(&engine, &QQmlEngine::quit, &QApplication::quit);
+    QObject::connect(
+        &engine, &QQmlEngine::quit, &app, &QApplication::quit, Qt::QueuedConnection
+    );
 
     // Set the debugMode properties depending of if we're running in debug mode
     // or not (`qmake CONFIG+=dev ...`, default in autoreload.py)