Added shortcut key to dock windows

Meta + [ / ] will dock top window to left / right or cycle
between 1/3 1/2 2/3 of screen if it's already in docking mode

Change-Id: I546418235a9b9699d406b04f52914c85bd950532
(cherry picked from commit 63635675b56564a17e3897a221d73a19cfbc77f7)