fix #913 cosmetic fix login dialog

fix #913 

I first wanted to replace it with a dialog instead of having a new activity with a FrameLayout but I then realised we would need some sort of progress dialog after the `PositiveButton` is pressed. So I kept the FrameLayout. 

I also tried to make the buttons look like native dialog buttons in af8ffba that works well but only for API >= 11 and the extra work to make it work on gingerbread doesn't worth it.