Improve error messages for invalid characters in variables names.
Make sure all time series are resampled: All time series are now resampled to avoid inconsistent results when date frequency is not data defined.
Simplify unit-definitions in Yaml (continuation of breaking change in v8.16): Write SM3_PER_DAY instead of STANDARD_CUBIC_METERS_PER_DAY. Write KG_PER_DAY instead of KILO_PER_DAY.
Fix error that occurs when creating error message related to wrong category for power from shore columns/variables (CABLE_LOSS and MAX_USAGE_FROM_SHORE only valid for category POWER_FROM_SHORE).