Import
- not importing f objects anymore, f is now used as an index
- deleting all 'ts_...' relationship imports, including timeseries parameters in other relationships instead, using Base_ts alternative
- importing node boundaries as mappings

Transformer
- not renaming parameters anymore

Export
- updating the exporter according to the importer changes
- exploiting the new feature to export multiple mappings to the same GDX "table"
- filtering value types when exporting constants and timeseries/mappings

The alternatives should be used differently.