Segmentation by difference between models' performance

[Firenze11]

Summary

Currently we have allow users to slice by baseCols, which can be one of:

1. feature columns
2. prediction columns
3. score/performance columns

But sometimes, especially in manual segmentation, something like the difference between two score/performance columns would be desirable.

Possible Solution

• Allow users to define column computation logic in UI, e.g. @score:0 MINUS @score:1
• Compute these columns once they are defined, append them to column list
• Allow deletion of these columns (in the database representation we will set it to null instead of actually deleting it, to avoid column index shift