Make tso_stub federate

[trevorhardy]

TESP already has a "dso_stub" federate used for looking at wholesale market operations. It would be helpful to have a "tso_stub" that could be paired with what DSO+T called the "substation" to look at retail operations. This federate functionally mocks the wholesale market operations by providing generic wholesale market energy cost curves that the retail market can play against. It would be helpful to be able to configure the "tso_stub" to be configurable such that the substation in question could be associated with particular times and places. For example, we could take data from the DSO+T BAU cases and allow the user to specific an 8-bus node and start time to use in the testing. The generator cost curve would have to be inferred from the simulation data but I suspect that wouldn't be too hard. Maybe the cost curve would be unique for each week of the year? Or every month?