Support mongodb repositories (alongside JPA in same configuration)

Hi,

I see from the Spring Data Rest front page that support for mongodb repositories is on the roadmap. I want to +1 this feature and watch so I can do some early testing ;-)

Also, it is worth adding an interesting use case, which is mongodb and JPA repositories in the same application. They work well together in Spring data generally, so it would be good to see the compatibility extend to the rest exporter. I raise this now because at the moment mongodb repositories have to explicitly marked with @RestResource(exported = false) to avoid the rest exporter throwing an exception for 'not an entity' on the @Document annotated class, so I guess there would be a need to detect the correct repository exporter to use for each repository.

Start with the Spring Data REST REST exporter and the repository handling around @RestResource(exported = false), @Document, and the 'not an entity' exception. Investigate how JPA and MongoDB repositories are identified in one application; done means MongoDB repositories export correctly alongside JPA repositories without requiring them to be disabled.