updated LinkedDataWebController so it always returns a Dataset, not a Model
changed linkedDataRestClient, linkedDataService and dependent classes to use Dataset instead of Model
updated utils to support Dataset in addition to Model
added visiting method returning NodeIterator
Merge branch 'feat-linkeddata-js' into devel

Conflicts:
	webofneeds/won-node-webapp/src/main/java/won/node/web/LinkedDataWebController.java