We were passing the *requesting* user's moved_to value to the Move notification template, instead of the id of the user that they are being notified about.
Additionally, the id_to_username template tag had no fallback for if the user_id is None.
This resolves both problems and removes an unnecessary space in a template for when the logged in user made the move.
Fixes#3196
* update User model to allow for moved_to and also_known_as values
* allow users to add aliases (also_known_as) in UI
* allow users to move account to another one (moved_to)
* redirect webfinger to the new account after a move
* present notification to followers inviting to follow at new account
Note: unlike Mastodon we're not running any unfollow/autofollow action here: users can decide for themselves
This makes undoing moves easier.
TODO
There is still a bug with incoming Moves, at least from Mastodon.
This seems to be something to do with Update activities (rather than Move, strictly).
