[workflow_concepts] Make it work with the workflow_concept
For now process is always call. When call from workflow_concept it insure the input has benn provided previously. Otherwise you should provide the xas_object. It might evolve with time. Add some simple unit test to insure an orangecontrib est workflow can be converted to a graph and a graph to an est workflow. Add test to insure we can execute it as well Make `Process` inherit from Task Create a OWESRFWidget which inherit from OWWidget and implement stuff for the task graph.