sidekiq-bulk's push_bulk can either accept arguments directly or run them
through a block.

Setting expectations on the result of evaluating the blocks allows testing
more code (the block itself) and the test is moved closer to the *interface*
of the tested code than its precise implementation.

* Change account and user fabricators to simplify and improve tests

- `Fabricate(:account)` implicitly fabricates an associated `user` if
  no `domain` attribute is given (an account with `domain: nil` is
  considered a local account, but no user record was created), unless
  `user: nil` is passed
- `Fabricate(:account, user: Fabricate(:user))` should still be possible
  but is discouraged.

* Fix and refactor tests

- avoid passing unneeded attributes to `Fabricate(:user)` or
  `Fabricate(:account)`
- avoid embedding `Fabricate(:user)` into a `Fabricate(:account)` or the other
  way around
- prefer `Fabricate(:user, account_attributes: …)` to
  `Fabricate(:user, account: Fabricate(:account, …)`
- also, some tests were using remote accounts with local user records, which is
  not representative of production code.

* Change move handler to carry blocks and mutes over

When user A blocks user B and B moves to a new account C, make A block C
accordingly.

Note that it only works if A's instance is aware of the Move, that is,
if B is on A's instance or has followers there.

* Also notify instances with known people blocking you when moving

* Add automatic account notes when blocking/muting an account that had no note

* Add UserNote model

* Add UI for user notes

* Put comment in relationships entity

* Add API to create user notes

* Copy user notes to new account when receiving a Move activity

* Address some of the review remarks

* Replace modal by inline edition

* Please CodeClimate

* Button design changes

* Change design again

* Cancel note edition when pressing Escape

* Fixes

* Tweak design again

* Move “Add note” item, and allow users to add notes to themselves

* Rename UserNote into AccountNote, rename “comment” Relationship attribute to “note”

* 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