allow localhost as an embeddedable host

app/models/embeddable_host.rb

@@ -25,7 +25,8 @@ class EmbeddableHost < ActiveRecord::Base
 
     def host_must_be_valid
       if host !~ /\A[a-z0-9]+([\-\.]{1}[a-z0-9]+)*\.[a-z]{2,7}(:[0-9]{1,5})?(\/.*)?\Z/i &&
-         host !~ /\A(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\Z/
+         host !~ /\A(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\Z/ &&
+         host !~ /\A([a-z0-9]+([\-\.]{1}[a-z0-9]+)*\.)?localhost(\:[0-9]{1,5})?(\/.*)?\Z/i
         errors.add(:host, I18n.t('errors.messages.invalid'))
       end
     end