Update Project and ProjectContent to match Brian's model

Gets rid of content field on Project API response and instead merges
the translated strings for the requested language into the API response
Add Project Content Endpoint For Translation

Partial solution for #122
Convert Strings to Symbols

cause MRI is picky
Constantize Project Content Params
Add Specs for translation scope and predicate
Add specs for new translator and primary predicates
Merge pull request #215 from edpaget/project-content-update

Project content update