added ERD custom setting for persisting diagrams
added ERDPersister to enable saving of diagrams for later re-use
removed commented to and adjusted to new API
Merge branch 'master' of https://github.com/stevebuik/GraphVizForce

# By Zhiren Guan
# Via Zhiren Guan
* 'master' of https://github.com/stevebuik/GraphVizForce:
  [Bug fix] Only generate ERD for selected groups, filter by checkboxes in VF page
  Updated ERDGeneratorPage Cosmetics, added edit button to select group

Conflicts:
	src/classes/ERDGeneratorController.cls