* Dont allow empty value in user allowed languages

* Sanitize language input to reject blank values in array

* Add option to disable two factor auth in admin accounts panel.
Closes #2578

* Add @mjankowski's suggestions.
* Moves destroy actions behind User#disable_two_factor!
* Adds spec coverage for Admin:TwoFactorAuthenticationsController and User#disable_two_factor!

* Stricter whitelist rules

* Linting

* Added spec for blacklisting

* Test subdomain blacklist on domain whitelist

* No need to split

* Change spec name

* Shows confirmed status in list.

* Adds ability to confirm users in admin UI.

* Added new english translations.

* Addresses feedback from #2245.

* More feedback.

* Add user spec for settings, highlight global default mutation issue

* Fix mutation issue caused by settings/preferences spec

* Add recovery code support for two-factor auth

When users enable two-factor auth, the app now generates ten
single-use recovery codes. Users are encouraged to print the codes
and store them in a safe place.

The two-factor prompt during login now accepts both OTP codes and
recovery codes.

The two-factor settings UI allows users to regenerated lost
recovery codes. Users who have set up two-factor auth prior to
this feature being added can use it to generate recovery codes
for the first time.

Fixes #563 and fixes #987

* Set OTP_SECRET in test enviroment

* add missing .html to view file names

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

Fixes #817