Halo: Add master switch to disable Halo (1/2)

-Port master switch from @Der-Schubi.
-Fixed Halo not showed at first notifiction pulldown.

Change-Id: I4ab22fe45353a00232617f0e835c88b15b2c6981
Signed-off-by: Dan Trifan <jimsth@gmail.com>
Merge "Halo: Add master switch to disable Halo (1/2)" into jb42