CoSES-Interface-Server datapoints

[JanAxelMayer]

According to the MEMAP-Datamodel the operational cost datapoint ('PrimEnCost') is mandatory also for storages.

This has to be added again in the next version of the CoSES Server and then the hardcoding - setting the value to 0.0 in #159 (ClientStorage.java) - has to be changed.

[thomaslicklederer]

ok
However, I thought that for the optimization the GenCosts would be the one that are relevant (als for couplers and controllable producers), not "PrimEnCost".