Operator result should be passed to view first
Currently, to execute an operator in the CMB application, one calls
pqSMTKModelPanel::requestOperation(). As part of this call,
handleOperationResult() is invoked. However, in order for operator views to provide feedback (e.g., why they aren't able to operate, show a preview of results), the view (especially any custom view widgets) should be given an opportunity to process the results and deny them to other observers.