Dar sprint 10

This branch contains work done during the sprint, it already went through code review and QA. Major changes
- DAR-147 chat support for preview environment
- DAR-351 chat security fix
- DAR-254 Forum activity module fix
- DAR-743 WAM Admins column lists non-admin user
- DAR-748 WikiaHome fix: filtering by vertical does not work properly 

This should be merged together with config changes in https://github.com/Wikia/config/pull/151