Make abtract element implement IGraphicItem to thwart GraphicDataProvider property inspection.
Add CoreNodes reference for RevitNodes to get DSColor.
Add ProtoInterface reference to RevitNodesUI to resolve IGraphicItem reference.
Merge branch 'ChocoButter-2Become1' of github.com:DynamoDS/Dynamo into ChocoButter-2Become1
Stub out tests for getting and setting parameters and overriding colors in view.
MAGN-2303. Unregister event handling when visualization update is paused.