Halo: Add master switch to disable Halo (1/2)
-Port master switch from @Der-Schubi.
-Fixed Halo not showed at first notifiction pulldown.

Conflicts:
packages/SystemUI/src/com/android/systemui/statusbar/BaseStatusBar.java

Change-Id: I93b59da79c63c3154bec1dba4490e4f4447a1564

Conflicts:
packages/SystemUI/src/com/android/systemui/statusbar/BaseStatusBar.java

Conflicts:
core/java/android/provider/Settings.java
packages/SystemUI/src/com/android/systemui/statusbar/BaseStatusBar.java