Configure/select index view column visibility

Allow the ability to toggle column visibility on index views. A configuration drop-down on appropriate index views could allow users to select which columns to view. This setting could be saved in the user preferences for individual users, and the default behavior might be defined either in CO Settings or by allowing the same drop-down widget to "Set as default" when exposed to CO Admins.

This behavior is specifically desired for the Organizational Identities index view but is likely applicable to others.