Notify app widget hosts when cross-profile providers change.

1. Notify the hosts in the group if a package gets white-listed or
   un-white-listed for providing widgets across profiles.

2. Notify hosts in the group for provider changes when a profile
   is deleted.

bug:17126070

Change-Id: Ic719c1c68e45842d50decc95603f1d61583b8f02