R1:aa3b2ec5dcd0

Give Pholio Images an authorPHID and use ExtendedPolicies to implement policy behavior

Summary:
Depends on D19912. Ref T11351. Images currently use `getMock()->getPolicy()` stuff to define policies. This causes bugs with object policies like "Subscribers", since the policy engine tries to evaluate the subscribers //for the image// when the intent is to evaluate the subscribers for the mock.

Move this to ExtendedPolicies to fix the behavior, and give Images sensible policy behavior when they aren't…