Design of the PreprId object model (in Java), and the entry point to the Spray REST API

There are three subprojects of the PreprId project:

1) PreprIdModelJava defines the objects of PreprId, their relations, and how they can be used as a basis for createing scalable pluggable domain models of entities, roles and permissions.
2) PreprIdAPI is a Spray REST API that should be running on api.preprid.org and acting as an entry point to the PreprId data. Currently, one file is really Prepr related and the rest are coming from the Activator template I used to boot strap the project.
3) PreprIdWeb is a Play framework web project, which should contain the Web UI for registering in PreprId as well as the admin interface. Currently this project is merely the Activator template I used to bootstrap the project.

PS: There was another Pull request submitted a few weeks ago, with a lot of bootstrapping files. This diff should have ideally been based off that pull request, so that the PreprId related changes are clear. However, I didn't know how to do that with GitHub given that the earlier pull request wasn't accepted yet.