Fix master specs and improve testing

[krzysiek1507]

1. Render errors partial for RelationTypesController
2. redirect back or default in RelationsController#destroy
3. update poltergeist to ~> 1.10 (support newer phantomjs)
4. update database_cleaner to ~> 1.5
5. test against ruby 2.2.5 and 2.3.1; test on postgres and mysql
6. fix specs