Multi-period development

[nailend]

This is an issue to collect necessary changes for the multi-period feature to actually replace single-period in the longterm.
Feel free to extend the list and discuss necessary changes in here.

• Align multi-period storage with TIMESTEPS and TIMEPOINTS (see First time step of storage_content sequence is missing #1030 and Revise indexing of date and time #811)
• Add option to set initial storage level (see Multi-period investment optmization: no investment in first period #1029)
• Make discounting optional/move outside solph (see Multi-period remaining value calculation #1018 and Use representative year for multi-year-periods in multi-period-investment #992)
• Add storage roundtrip conditions
• fixed capacity for Multi-period (make arrays for nominal_value possible)
• Provide information on length of last period (see Implausible diverging results comparing 1-year-multi-period & multi-period optimization #1047)

[jokochems]

Hey there, I'd be happy to discuss and assist in the further development. My current limitation is just, that my time is pretty much limited and framework development is not my top priority currently. I'm fairly confident that it will be better in a couple of months.

If there are questions on the current status quo, feel free to approach me (as you already do). And many thanks for collecting the stuff here. 😀