The query is very inefficient without any constraints on large sites and
the average of all time to first response since the beginning of time is
not useful as well.
We want to put the name of the trust level in to generated URLs, not the human-readable form.
i.e.:
`/admin/users/list/newuser`
rather than:
`/admin/users/list/new user`
Refactors `TrustLevel` and moves translations from server to client
Additional changes:
* "staff" and "admin" wasn't translatable in site settings
* it replaces a concatenated string with a translation
* uses translation for trust levels in users_by_trust_level report
* adds a DB migration to rename keys of translation overrides affected by this commit
