MultiUser: Bring support to our features

Implements long-overdue support for multiuser in key areas.

Points of interest:
 * UserHandle.USER_CURRENT can only be used in getting a setting
 * Status bar is recreated on user switch to load quick settings tiles
    * May change in the future for less performance impact

Signed-off-by: Evan Anderson <evan@thelinuxman.us>
Change-Id: I9659f7f761850fdbe1be500fe784c30aea82d03d