Don't start band select on empty grid.

Masks an issue in band controller resulting in index out of bounds exceptions.
Eliminate the need to cast helper when constructing BandController.
Improve naming of Band related classes for clarity of purpose.
Normalize some "helper" class method names.
Rename BandSelectModelTest to match existing convention for tests on inner classes.

Bug: 23905473
Change-Id: Iaf7604fb729cf563a04dc92d78b24e2fe4812abe