Ssc 1123 price signals to retail rate naming

[brtietz]

Rename price signals dispatch to retail rate dispatch, bringing the old "forecast" enum along the way.

Fixes NREL/SAM#1123

Companion SAM PR:

Should be good to go if the tests pass, but any additional searches for "price signals" as a spot check would be appreciated.

[cpaulgilman]

Looks good. Pointing out some additional variables, not sure if these need changing.

• "Price signal" in comment of lib_utility_rate.cpp:

  ssc/shared/lib_utility_rate.cpp

  Line 357 in 091de1b

  // Ignore any peak charges lower than the average gross load - this prevents the price signal from showing demand charges on the first hour of each month when the load is not really a peak

• Also forecast_price_series_dollar_per_kwh in cmod_battery.cpp/h is for FOM battery, but I think refers to retail rates for electricity purchases,

  ssc/ssc/cmod_battery.cpp

  Line 621 in 091de1b

  forecast_price_signal fps(&vt);

• forecast_price_signal class in common.h

• vtab_forecast_price-signal in cmod_pvsamv1.cpp

[brtietz]

@cpaulgilman Thanks! I clarified that first comment to "retail rate forecast." The other three variables are for the front of meter automated dispatch, so I'll leave those alone.