Fixes #4478 - Added API localization

Do not merge before new apipie-rails 0.2.0 with this PR https://github.com/Apipie/apipie-rails/pull/232#issuecomment-42522666 is available.

This PR contains 
- localization setup for apipie
- updated deps on apipie 0.2.0
- strings from apipie-rails to be included to our translation process
- all the API doc strings wrapped into _()