Add option to disable two factor auth in admin accounts panel. (#2584)

* 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!

config/locales/en.yml

@@ -84,6 +84,7 @@ en:
       public: Public
       push_subscription_expires: PuSH subscription expires
       reset_password: Reset password
+      disable_two_factor_authentication: Disable 2FA
       salmon_url: Salmon URL
       show:
         created_reports: Reports created by this account

config/routes.rb

@@ -89,6 +89,10 @@ Rails.application.routes.draw do
       resource :suspension, only: [:create, :destroy]
       resource :confirmation, only: [:create]
     end
+
+    resources :users, only: [] do
+      resource :two_factor_authentication, only: [:destroy]
+    end
   end
 
   get '/admin', to: redirect('/admin/settings', status: 302)