- Converting samples and time steps into indices when storing p_s_discountFactor, sGroup, gnss_bound, uss_bound, t_invest, and utAvailabilityLimits.
- Storing sGroup, gnss_bound, uss_bound, t_invest, and utAvailabilityLimits as boolean parameters of group, grid__node, unit, model, and unit object/relationship classes, respectively.
- Adding a 'model' object class for t_invest and p_s_discountFactor.

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.

Updating SpineDB to Backbone input GDX Exporter. Works with the current Backbone version, at least if there is data in every set and parameter.