Fixes

- Add .json to GET /contents/UUID@draft
- Update GET /contents functional test to check against every field
- Add 'version': 'draft' to document
- Rename Document.contents to Document.content
- Change default language from en-us to en
- Rename Document.summary to Document.abstract
- Return "application/vnd.org.cnx.module" for Document mediaType
- Add CORS headers Access-Control-Allow-Credentials and Access-Control-Allow-Origin

The CORS headers commit allow cookies to be sent to the backend server from javascript.  So we shouldn't need to change the cookie domain anymore.