Cleanup unused using statements.

Conflicts:
	src/DynamoCore/Models/HomeWorkspaceModel.cs
Do not run the expression when shutting down.

Conflicts:
	src/DynamoCore/Models/DynamoModel.cs
	src/DynamoCore/Models/HomeWorkspaceModel.cs
Remove a debug print.
Remove a debug print.
Remove one more debug print.
Add null checks.

Avoid attempting to load trace data if the engine controller is null.