* Fix being able to import more than allowed number of follows

Without this commit, if someone tries importing a second list of accounts to
follow before the first one has been processed, this will queue imports for
the two whole lists, even if they exceed the account's allowed number of
outgoing follows.

This commit changes it so the individual queued imports aren't exempt from
the follow limit check (they remain exempt from the rate-limiting check
though).

* Catch validation errors to not re-queue failed follows

Co-authored-by: Claire <claire.github-309c@sitedethib.com>

* Add bell button

Fix #4890

* Remove duplicate type from post-deployment migration

* Fix legacy class type mappings

* Improve query performance with better index

* Fix validation

* Remove redundant index from notifications

* Fix being able to follow oneself by moving to an account that was following the old one

* Add specs

* Add spec to catch MoveWorker issue with local followers following both accounts

* Fix move worker breaking when a local account follows both source and target accounts

* Fix migration from remote to local account not sending Undo Follow

* Fix show_reblogs not being preserved for moved account's followers

Don't put Move handler on cooldown if it didn't run. Skip unmerging
from timelines to save unnecessary work.