[key event focus handling] Cleanup/Refactor/Feature

1) Focus navigation handling is refactored to Focus utility class.
New 2 step dpad navigation algorithm is inside Focus class
2) Introduced a map (or matrix) that indicates where sparse icons are located inside a grid.
This enables getting rid of the icon sorting logic which was costly.
3) Unified all the dpad handling logic inside the handleXXKeyEvent methods
4) DOWN/UP key will allow navigation between workspace icons and the hotseat
5) Folder icons allow DOWN/UP to navigate to the title

b/19381790

Change-Id: Id45b3f215ef7c1ca5f99b08e3d721e219298627a