Introduce forwarding intents across profiles.

The package manager service maintains, for some user ids, a list of forwarding intent filters.
A forwarding intent filter is an intent filter with a destination (a user id).
If an intent matches the forwarding intent filter, then activities in the destination can also respond to the intent.

When the package manager service is asked for components that resolve an intent:
If the intent matches the forwarding intent filter, and at least one activity in the destination user can respond to the intent:
The package manager service also returns the IntentForwarderActivity.
This activity will forward the intent to the destination.

Change-Id: Id8957de3e4a4fdbc1e0dea073eadb45e04ef985a