Suggestions to improve naming and consistency of stability indices

we came across the limitation, that it is not possible to calculate rta and ssi. This gives some complications if both params are needed.

While analysing the current situation where stability index are written, we came to the following suggestions:

• Remove Stability Indices from Timeseries (or coherent naming)
  • use ProfileMinimumStability instead
• add minimum_structural_stability_index on ProfileMinimumStability
• rename s5 -> liquid_water_index
  • and move to Profile ? or maybe not
• separate Parameter for RTA -> remove config SSI_IS_RTA (we want to calculate both)
• better parameter naming:
  • stability_index -> skier_stability_index (as well for ProfileMinimumStability) or use consistently sk38, sn38 and ssi

Open Question: Does SSI_IS_RTA currently control the output to S4 in smet AND ssi(0604) in .pro files ?

@nwever fyi