Created a ACTION_RESTRICT_BACKGROUND_CHANGED intent.

This intent will be broadcasted when:

- Global restrict background setting is changed (sent to all packages)
- An individual uid is added to or removed from the whitelist (sent just
  to the packages belonging to that uid).

This intent is only sent to registered receivers.

BUG: 26451391
Change-Id: Ic0a5771f88baa52076ad04764f29098a386463cc