Add recovery code support for two-factor auth (#1773)

* 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

app/views/settings/two_factor_auths/show.html.haml

@@ -8,3 +8,8 @@
     = link_to t('two_factor_auth.disable'), disable_settings_two_factor_auth_path, data: { method: 'POST' }, class: 'block-button'
   - else
     = link_to t('two_factor_auth.setup'), new_settings_two_factor_auth_path, class: 'block-button'
+
+- if current_user.otp_required_for_login
+  .simple_form
+    %p.hint= t('two_factor_auth.lost_recovery_codes')
+    = link_to t('two_factor_auth.generate_recovery_codes'), recovery_codes_settings_two_factor_auth_path, data: { method: 'POST' }, class: 'block-button'