Removed "NodeViewModel.OldValue" property
Removed "EngineController.GetStringValue", it's not referenced
Fixed deadlock in Watch3DView.VisualizationManagerRenderComplete
Merge branch 'master' of https://github.com/DynamoDS/Dynamo into OldValueMustDie
Merge pull request #2908 from Benglin/OldValueMustDie

Removed "NodeViewModel.OldValue" property
Merge pull request #2941 from Benglin/DeadLock

Fixed deadlock in VisualizationManagerRenderComplete
Merge branch 'master' of https://github.com/DynamoDS/Dynamo