Removed original login screen, made the new login screen a tab.
Removed guest tab (and started to use a checkbox for that for now).
Work in progress.
Renamed StoryModeLobby to UserScreen.
Fixed login problems (e.g. only online log in worked), improved handling
of error message, removed need for m_login_successful.
Select the current player by default.
Added 'delete player' functionality.
Added rename functionality.