add rdf:type for primary and mixin nodetypes and their supertypes

generate rdf types for primarytypes,mixins, and their supertypes
also a fix for a existing failing ITTest where adding a datastream was returning a HTTP 500

https://www.pivotaltracker.com/s/projects/684825/stories/65210272

in place of:
https://github.com/futures/fcrepo4/pull/237