webui: remove mixed indentation in App and LoginScreen
    
    Only spaces should be used for indentation.
    
    It was introduced in commits:
    
    * 7f9f59bae2a362ce945c49ad8342393b7a5c024f
    * 5d8fde0ac1a43c8f3dbc53b44d69f3663a8b36fb
    
    Related to: https://pagure.io/freeipa/issue/7559
    
    Signed-off-by: Petr Vobornik <pvoborni@redhat.com>
    Reviewed-By: Tibor Dudlak <tdudlak@redhat.com>