Add ransack support

solves #49

Author: ksemuldie

lib/active_admin/mongoid/document.rb

@@ -67,6 +67,17 @@ def group_by *args
       scoped
     end
 
+    def ransack *args
+      scoped
+
+      scoped.class.class_eval do
+        def result
+          self
+        end
+      end
+
+      scoped
+    end
 
 
     # Cache