add cost for increased battery life depletion when sitting at very high or low SOC

[ekkea]

added feature that allows to specify a cost for batteries sitting at very high or very low SOC for longer time.

added optional cost parameters to battery API:

• prc_dpl_soc_high:
  Price in €/h for higher battery life depletion when sitting at high SOC.
  A linear cost model is applied, starting at 80% SOC, applying full price at 100% SOC
  The battery capacity is assumed to be s_capacity or s_max if s_capacity is not specified.

• prc_dpl_soc_low:
  Price in €/h for higher battery life depletion when sitting at low SOC.
  A linear cost model is applied, starting at 20% SOC, applying full price at 0% SOC
  The battery capacity is assumed to be s_capacity or s_max if s_capacity is not specified.

The feature is tested and works as expected, however, it is not clear how useful it is as the optimization time horizon is short in relation to time duration needed to create noticeable life time depletion.