Add support for visualizing secondary users.

This functionality adds the secondary users to the screen, but
currently does not populate the information for them. Once the
external stats query works, I will add a loader which will
populate this information.

This also does not cover work profiles. Support for that is
forthcoming.

Bug: 34715777, 34225103
Test: Settings Robotest
Change-Id: Ib9b692b214f5ce5d303dfd64516381443d4acebd