UP-4280 : Enhance REST API with various features

UW added some things to the REST api for uPortal including:
+ A *marketplace* REST controller to: get the marketplace entries, get ratings by a user, post ratings given by a user
+ `/layoutDoc` now has an optional tab parameter which will filter the resulting portlets to be only for a specific tab
+ `/layoutDoc` now supports the alternative max url
+ `/layoutDoc` now supplies icon URLs
+ `/session.json` now has session key, uPortal version, and server name