Apub local object handling (#1297)

Apub local object handling (#1297)

* Limit visibility of some traits and methods

* WIP: alternative way to handle non-local object parsing

* finish this

* cleanup

* Move check for locked post into Comment::from_apub()

* Mark user as updated after fetching

* Should set last_refreshed_at, not updated

* Add ApubObject trait in DB, with method read_from_apub_id()

* Create shared, generic implementation for `FromApub`, prefer local data

* Check for community ban when parsing post/comment (fixes #1287)

* Fix tests (changes in get_object_from_apub() prevented `Update` from working)

* Support parsing `like.object` either as URL or object

* Send out like.object as URL, instead of full object (fixes #1283)

* add todo