REACH-31: Implement session manager

Pool of `DynamoViewModel` is created to minimize delay for a newly connected user. Server works in headless mode as a side effect of these changes.
You may want to do the following:

1. Set all ```WorkspaceModel.Model.HasUnsavedChanges``` to ```false```.
2. Call ```DynamoViewModel.ExitCommand.Execute(false)``` to shutdown the view model and model.