Fix mang-3188: dynamo hangs in opening for some custom node

The defect is because of two issues.

1. First issue is because of null reference exception. Opening a .dyn file will reset engine controller and recompile all custom nodes. As the recompilation happens inside the constructor of engine controller, at this point engine controller hasn't been created yet, so if the recompilation triggers some functions which use engine controller, a null reference exception will be thrown out.

2. Second issue is the controller tries to compile proxy custom node. 

So the fix is to remove ```CustomNodeManager.RecompileAllNodes()``` out of EngineController's constructor and skip the custom node compilation if it is a proxy node. 
The fact that these two lines appear next to each other multiple times might warrant refactoring into a separate, private method.