Added RevitNodes and RevitNodesUI projects

Link issue: http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4285
@Sharad, after the PR https://github.com/DynamoDS/DynamoRevit/pull/5 gets merged, Please review this one
Does DynamoUnits project has any dependency on Revit? If yes then that should be part of DynamoRevit and then we should reference from project and not from $(DYNAMOAPI)