Allow different types of heat pumps and stratified thermal storages in one energy system

[SabineHaas]

Should this part (3. Replace...) maybe be done for all storages in stratified_thermal_storages?

This would be nice. But for now there is only one file stratified_thermal_storage.csv. Its parameters are used in the precalculations. So storage_xx does not change over different storages in stratified_thermal_storages. It's the same as with the heat pump. There as well we unfortunately can so far provide only one heat pump type in heat_pumps_and_chillers.csv. 🙁

Originally posted by @MaGering in #148 (comment)

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We could allow to provide the column name of the heat pump from energyConversion.csv in a newly introduced column heat_pumps_and_chillers.csv.
In stratified_thermal_storage.csv we could use the storage_filename given in energyStorages.csv.