Update default CLI parameters of the launcher

* Use command syntax and double-dashes to be in-line with what Syncthing's
  help text suggests
* Drop the `--no-restart` parameter; I probably only added it after
  checking what flags the systemd-unit file specifies. However, the
  systemd-unit file specifies `--no-restart` only because restarts are
  handled by systemd in that case. For the launcher of Syncthing Tray it
  makes probably more sense to keep restarts enabled by default.

syncthingwidgets/settings/settings.h

@@ -91,7 +91,7 @@ struct SYNCTHINGWIDGETS_EXPORT Launcher {
 #else
         QStringLiteral("syncthing");
 #endif
-    QString syncthingArgs = QStringLiteral("-no-browser -no-restart -logflags=3");
+    QString syncthingArgs = QStringLiteral("serve --no-browser --logflags=3");
     QHash<QString, ToolParameter> tools;
     bool considerForReconnect = false;
     bool showButton = false;