* Stricter whitelist rules

* Linting

* Added spec for blacklisting

* Test subdomain blacklist on domain whitelist

* No need to split

* Change spec name

* Add `Presenters` group to SimpleCov configuration

* Move validators to app/validators, add to simplecov config

This adds the ability to filter user signup with a whitelist
instead of or in addition to a blacklist.

Fixes #817