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.

index.html

@@ -680,7 +680,7 @@
                             Close
                         </button>
                         <button
-                            type="button"
+                            type="submit"
                             class="btn btn-primary"
                             form="loadedittrackForm"
                             data-i18n="trackasroute.title"
@@ -800,7 +800,7 @@
                         </button>
 
                         <button
-                            type="button"
+                            type="submit"
                             class="btn btn-primary"
                             form="loadNogosForm"
                             data-i18n="loadNogos.load"