Disable Devise sign ups if Guisso is enabled

If we offload authorisations to Guisso, then avoid local users sign ups.
Guisso is CAPTCHA-protected, so we'd rather use it for production than add
CATPCHA protections to each InSTEDD app.

Author: matiasgarciaisaia

config/routes.rb

@@ -29,7 +29,7 @@
 
   scope "(:locale)", :locale => /#{Locales.available.keys.join('|')}/ do
 
-    devise_for :users, :controllers => {
+    devise_for :users, :skip => [ ( :registrations if Guisso.enabled? ) ], :controllers => {
       :registrations => 'users/registrations',
       omniauth_callbacks: "omniauth_callbacks",
       sessions: "sessions"