refs https://github.com/TryGhost/Toolbox/issues/309
- this commit adds a validation array of valid user `status` values to
the schema
- this also includes a migration to update users with invalid statuses
to `inactive`, which I've seen with `invited` and `invited-pending`
statuses that pre-dated proper invitations
- this also deletes tests that were wrong and written 7 years ago before
invites was added