add WEO 2023 free data to historical.mif

[fbenke-pik]

• this PR adds the 2023 free data to historical.mif

• renames functions for consistency with future data updates (read/convert/calc: IEA_WEO_2021 -> IEA_WorldEnergyOutlook)

• refactors calcOutput function to use a custom aggregation function

• fixes a bug in convert function:

  • before: convert function disaggregates EU to countries according to a weight, but then sets GIB to 0
  • values should be slightly higher after this bugfix
  • this also affects calcFeDemandIndustry cc @0UmfHxcvx5J7JoaOhFSs5mncnisTJJ6q