Work on separating out the status bar management

Lots of stuff:
 - Make StatusBarIconController be a permanent dependency
 - Break out dark stuff into DarkIconDispatcher
 - Create StatusBarFragment
   - This bit is a bit ugly for now, but will be better later
 - Other stuff probably

Test: runtest systemui
Change-Id: I4973bc9f944e66af92731bf1edd2b39657f1782f