Flash Notifications: make sure proximity sensor gets unregistered if the feature is shut off

Also refactor code slightly to make more sense-- not all members need to be in the outter class

Change-Id: I70c2145556badfbebb487f40a0e8c3362ad9b251
Flash Notifications: clean up register/unregister methods

PS2: add missing boolean preventing the feature from being turned
off

Change-Id: I87b639b50e668deae35550c96b2c82b0e67fd3d2
Merge remote-tracking branch 'upstream/EXODUS' into EXODUS