rollup "group" column behaviour should be optional

[dsmmcken]

As a user I want more control over how this is rollups are displayed in rlation to #1555. For some tables it doesn't make sense to use the new grouping style. Further, if there's only one column, it's redundant and doesn't need to be displayed separately at all, however it would still be different then the previous in that it wouldn't repeat values down the column.

• [x] #1831
• [ ] #2128
• [x] #1853
• [ ] #2129

Example with one column, group should display the column directly, and be filterable/sortable, but not fill column values.