If you turn it on now, default all users to approved since they were
previously. Also support approving a user that doesn't have a reviewable
record (it will be created first.)
This also includes a refactor to move class method calls to
`DiscourseEvent` into an initializer. Otherwise the load order of
classes makes a difference in the test environment and some settings
might be triggered and others not, randomly.
"Rejecting" a user in the queue is equivalent to deleting them, which
would then making it impossible to review rejected users. Now we store
information about the user in the payload so if they are deleted things
still display in the Rejected view.
Secondly, if a user is destroyed outside of the review queue, it will
now automatically "Reject" that queue item.
Conversely, if a user is deactivated the reviewable should automatically
be rejected.
Before this fix, if a user was not active they'd still show in the
review queue but without an "Approve" button which was confusing.
