Cleanup keyboard code.

This should be the last keyboard CL.
- Fix bug: couldn't focus All Apps button in some cases when the All
Apps column was skipped over. Also added test case for this.
- Stop explicitly passing countX and countY to handleKeyEvent, as
these had to match the matrix dimensions anyways.
- Rename createSparseMatrix() - there were 3 methods of the same name,
but all had different purposes. This is confusing both from a
readability standpoint and also when looking at stack traces.

Change-Id: I08ba8411674fcea43a608856c114dee8dbd22398