change displayed items in plot "Total power"

[stefansc1]

• no more individual loads like batteries
• sum of all battery powers (if any batteries are present)
• one line for every GC (if more than one GC)

[jakobgemassmer]

Proposal: We enter the totals of all loads in the plot under "Total Power". In other words, the sum of all CS (already the case), all stationary batteries, all "Local Generation" and all fixed loads. And also "Total" (which is already there). This would not really change anything for individual SpiceEV simulations (unless you are simulating with several fixed loads or similar). It would even be "nicer" because, for example, the name of the CSV of a "PV time series" would no longer appear in the legend, but only "Local Generation".