Introduce new 'loggedin' mode

We want to enable some features only to logged in users. This mode
allows that.

Additionally, there is no need for setEnabled() is the user IUserMode
interface, as not all modes are selectable by user.

Bug: T232594
Bug: T232652
Change-Id: I2138472e68d8cab1c50cbb42807bd5b79e7e2749