Allow Return key to accept dialog when loading no-go areas or track as route

After ca53080e added Return key handling to the "Delete route" dialog, only
the "Load no-go areas" and "Load track as route" dialogs were still missing
similar functionality.

The implementation is based on 2a431932.

Test Plan:
- Open "Load no-go areas" or "Load track as route" dialog.
- Press Space or Return to open file dialog, choose file,
  Tab out of file input and press Return to confirm modal.
- Notice not having to Tab to the respective confirmation button.

js/plugin/RouteLoaderConverter.js

@@ -191,7 +191,8 @@ BR.routeLoader = function (map, layersControl, routing, pois) {
                 }.bind(this)
             );
 
-            L.DomUtil.get('submitLoadEditTrack').onclick = L.bind(function () {
+            L.DomUtil.get('submitLoadEditTrack').onclick = L.bind(function (e) {
+                e.preventDefault(); // prevent page reload on form submission
                 this._closeCanceled = false;
                 this.onBusyChanged(true);
                 if (this._testLayer.getLayers().length > 0) {