Some ActivityPub servers refuse to embed remote objects into their own
output. This is because they are not the authoritative source for these
objects, and as such embedding them is always a waste of space. The
follow request and follow models contain a URI, so this can be used to
match them.

* Allow to dereference Follow object for ActivityPub

* Accept IRI as object representation for Accept activity

- Tries to avoid performing HTTP request if the keyId is an actor URI
- Likewise if the URI is a fragment URI on top of actor URI
- Resolves public key, returns owner if the owner links back to the key

* Handle ActivityPub follows correctly

ActivityPub follows are follow-requests. Always require an Accept.
If account is not locked, auto-accept.

* Handle ActivityPub Accept/Reject-Follow

* Fix wrong method

* Fix wrong class