Fixes for rails 4, mongoid 4, ransack and activeadmin 1.x

Removed
- meta_search
- comment

This commit works with active_admin 1.x,  [ransack](https://github.com/activerecord-hackery/ransack) and mongoid 4. [Mongid support](https://github.com/activeadmin/activeadmin/issues/2714#issuecomment-61929424)