SECURITY: Prevent preference intents from exploiting settings.

Settings has super powers because it shares the system uid. We prevent
those powers from being exploited by malicious authenticators by
checking the intents those authenticators provide.

We will only launch intents that resolve to Activities that are exported=true
or owned by the same UID as the authenticator.

Bug: 14408627
Change-Id: Ia179df8561d29745767dac0f3c97eb0f68083f59