Rename BandController. Make GridModel top level.

Renaming for consistency with GestureSelector.
Move GridModel to own file since it's a fairly large class.
No content changes save moving NOT_SET constant to GridModel.

Bug: 64847011
Test: Passing.
Change-Id: I9f5900ba65a61800c6c26ffe1fd0aded65e9f957
10 files changed