Consolidate statusbar/notification and notification/

Move everything to notification/ in SettingsLib. Also have all
corresponding tests as deviceless tests in the correct directory.

I also fixed some style issues because the presubmit hook was
complaining.

Bug: NA
Flag: EXEMPT trivial refactor
Test: existing tests pass
Change-Id: Icd464566b60d1c219892c35cd17abe104017b3fb