pump_electricity_zo variables should be indexed by time

[tarnold17]

In pump_electricity_zo.py, most of the variables are not indexed by time. They should be updated so they are indexed by time.

[dangunter]

@TimBartholomew : all operating costs should be indexed by time.

Need to add an issue in IDAES

[andrewlee94]

@dangunter Whilst operating costs should be indexed by time to allow them to vary, that then opens up the question of how you sum them over time. That should be done by integrating the costs over time, but at least last time I asked about that Pyomo told me that they didn't have good tools for that yet (this is separate from the time stepping integrators/simulators we use for solving the problem). So, we might need to talk to the Pyomo team first.