Add new GridModel hideGroupedColumns and showUngroupedColumns config

[petradish]

Resolves #1369

• This was a lot trickier than I already expected. Needs more work/consideration.
• Setting the ag-grid flag suppressMakeColumnVisibleAfterUnGroup= true seems like the best way to allow us to control column visibility.
• There is a degenerate case where the combination of hideGroupedColumns = true && showUngroupedColumns = false can permanently hide a column with excludeFromChooser = true && hidden = false. I added a warning for this case -- not sure what else to do there.

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• Caught up with develop branch as of last change.
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• Reviewed for breaking changes, added breaking-change label + CHANGELOG if so.
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