Nested Grouping

This include the code fix with 50k rows
Revert "Nested Grouping"

This reverts commit 1efc84f99fb12c1c2994abeaa66c2ba5cdbe4441.
Nested Grouping with 50k rows

This is working with a .groupby String to expand/collapse.
Ex.: dataView.expandGroup("duration:10-->percentComplete:55");