Expose the underlying Project's ClassLoader via a new ProjectFacet

https://github.com/picketlink/picketlink-forge-addon/blob/master/impl/src/main/java/org/picketlink/tools/forge/operations/PersistenceOperations.java#L204

Some Addons need to be able to ClassLoad projects in order to reflect on types in dependencies. This is likely a dangerous operation, however, since it can lead to ClassLoader memory leaks, so some protection/patterns will need to be put in place to make this less likely.