* [feature] Federate interaction policies + Accepts; enforce policies
* use Acceptable type
* fix index
* remove appendIRIStrs
* add GetAccept federatingdb function
* lock on object IRI
* update Activity
* add instance-deliver-to-shared-inboxes setting
* update activity version again
* add SharedInboxURI field to accounts
* serdes for endpoints/sharedInbox
* deliver to sharedInbox if one is available
* update tests
* only assign shared inbox if shared domain
* look for shared inbox if currently nil
* go fmt
* finger to get params.RemoteAccountID if necessary
* make comments clearer
* compare dns more consistently
