Application restrictions API

Adds the ability for apps to export some restrictions. The restrictions
are presented in Settings based on the restriction type. The user's
selections are stored by UserManagerService and provided to the
target user's application as a list of RestrictionEntry objects which
contain the key, value(s).

Also introduce a manifest entry for system apps to request that the
app be automatically installed in all users, so that they cannot be
deselected by the owner user.

Shared account filtering for non-whitelisted apps.

Change-Id: I15b741e3c0f3448883cb364c130783f1f6ea7ce6