Set APC correctly for community updates, reject routes for non-APC comms

Set APC correctly for community updates, reject routes for non-APC comms

When an APC community update is received, the "apcs" list is empty. The
APC for any realms described by that update should be the APC community
itself.

Also, the trust router previously accepted any realm/community pairs for
routing. That should have been APC communities only.

Finally, this also prevents configuring multiple communities with the
same ID.