Use sticky broadcast to convey torch state (1/2).

It doesn't really make sense to store the (non-persistent) state of the
torch in a (persistent) setting. As the torch is sending a broadcast
anyway, make that broadcast sticky and use it to convey the state.

Also unify the torch constants (actions, extras, activity names) at a
common place.

Change-Id: I5d6d7a2b731c2300ec4dd6c678372e9cb2870b16