Export import varaibles / based on NAVIGATE / ENGAGE
This PR adds Export Import variables from NAVIGATE / ENGAGE
Some macro sectors are missing but will dynamically change by updating the tag (#279 ) Export|Energy Export|Industry|Chemicals Export|Industry|Manufacturing Export|Industry|Energy Export|Other Export|Industry|Energy Intensive
Discarded (can be computed within the database): Exports|% change per GDP Export|Developing Country Share Exports|% change from Ref
Having second thoughts, I am moving export and import variables to the trade.yaml files and improve clarity of the use of variable name with a header
Looking at NAVIGATE and ENGAGE "Trade" variables, I further discarded: "Trade|Emissions|Value|Carbon*" variables (redundant with "Trade|Emissions Allowances*" "Trade|Gross Import|Secondary Energy|Electricity|*": we can add Export and Import of energy in a further release
@volker-krey @macflo8 This a good example on implementing both ISIC sector nomenclature and biophysical nomenclature. The same can be done for Production, for exampel.
Done, I also changed tier to Tier 2 @danielhuppmann
@danielhuppmann I think this has been reviewed and coul dbe merged
@danielhuppmann A kind reminder to merge this.