Fix MAGN-4095 Getting crash while running Document after closing and reopening again.

@lukechurch

This submission fixes the crash when Dynamo tries to read trace data using SoapFormatter. The formatter will require the type information related to the object to be desialized and it will try to load the assembly. But unfortunately if we close the plugin, the resolver is removed. As a result, the assembly will not be found and the formatter will throw an exception. Ideally the resolver should be removed when the plugin is shutdown. This submission makes the fix the remove the resolver at the right time.
The fix makes sense. I'm not 100% sure this is good event handling practice though. If we move the un-registration of the event handlers to shutdown, but every time we start Dynamo we register a handler, we will have an imbalance in the registration/un-registration of the event handlers.