Cost units for control optimization may be wrong

It came to my attention in reviewing #463, that the cost units for the control optimization may not make sense. Specifically, in pyomo_controllers.py, we have

       '''
        cost_per_production (float):
            The cost to use the incoming produced commodity (in $/commodity_rate_units).
        cost_per_charge (float):
            The cost per unit of charging the storage (in $/commodity_rate_units).
        cost_per_discharge (float):
            The cost per unit of discharging the storage (in $/commodity_rate_units).
        commodity_met_value (float):
            The penalty for not meeting the desired load demand (in $/commodity_rate_units).
       '''

which means when the rate units are kg/h, the cost units would be in USD/(kg/h). If these unit are correct, we should improve the explanation so someone like me is not confused in the future. I would particularly appreciate your thoughts on this @genevievestarke.

Review the cost parameter documentation in pyomo_controllers.py and trace how those values are used in the control optimization. Determine whether the stated units are dimensionally correct; done means either correcting the units or improving the explanation so the cost interpretation is unambiguous.