It's very easy to forget to add `require 'rails_helper'` at the top of every core/plugin spec file, and omissions can cause some very confusing/sporadic errors.
By setting this flag in `.rspec`, we can remove the need for `require 'rails_helper'` entirely.
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
David Taylor
Phil Pirozhkov
Jarek Radosz
Gerhard Schlager