Table: extend aggregate module by preprocessing

[mw25]

Issue

These are the modifications of OrangeTableGroupBy and Table.groupby() to allow preprocessing / range selection for each group, mentioned in #5541 (comment)

This allows preprocessing via scripting. Optionally, one could make a widget that is based on this.

Description of changes

The Table.groupby() functions gets a new parameter with which the preprocessing can be set.

Includes

• Code changes
• Tests
• Documentation

[PrimozGodec]

Thank you for your contribution.

I would prefer it if the implementation of aggregate remains as it is. Since aggregation is a two-step operation one can extend this module when needed and add preprocessing there.

For example, if that kind of preprocessing is required in a time-series add-on, group-by can be extended there.

[janezd]

We discussed this today at live meeting. We agreed with what @PrimozGodec wrote above.