In single-room mode, refreshing the page always sends user to session picker

[psrpinto]

Since #193, when single-room mode is enabled, and user has multiple sessions, chatrix no longer remembers the screen the user was on, and always sends them to session-picker.

This happens in one (or both) of the following scenarios:

1. User first logs in as guest, and then as a "normal" account, since the guest session remains available.
2. User signs in to multiple "normal" accounts.

[ashfame]

I suppose we should log out of the guest session as soon as a login is successful.