Enable LDAP api. Add LdapGroup entity to api

lib/api/api.rb

@@ -38,5 +38,6 @@ module API
     mount ProjectSnippets
     mount DeployKeys
     mount ProjectHooks
+    mount Ldap
   end
 end

lib/api/entities.rb

@@ -136,5 +136,9 @@ module API
       expose :target_id, :target_type, :author_id
       expose :data, :target_title
     end
+
+    class LdapGroup < Grape::Entity
+      expose :cn
+    end
   end
 end