Added File and Image Migration Handlers to osha migration
Made publication cover image multilungual
Updated publication migration to support file and cover_image multilingual refs #2680
Refactored migration publication test to check for multilingual files. Refactored test data folder refs #2680
Fixed Field Handlers bug in publications migration
Merge pull request #89 from dragos-dumi/2680_update_publ_migr_cover_img

2680 update publ migr cover img