ActivityFromPost creates a new (ActivityPub) `Activity` instance derived from 'acct', 'post' and 'post_tags'.

AddPost creates a new post record for 'body' and adds it to the post database.

GetPostFromObjectURI attempt to derive a `Post` ID and its matching instance from an (ActivityPub) object URI.

NoteFromPost creates a new (ActivityPub) `Note` instance derived from 'acct', 'post' and 'post_tags'.