Add inbox folders / tabs for management

[aawiseman]

The ability to add Inbox folders or tabs that separate MR challenges would help clean up MR inboxes. Long lists of completed challenges I posted, complete challenges I worked on but didn't post, and reviewed tasks can be difficult to sort through.

Perhaps splitting notifications into a ‘Completed’ and ‘Revisions’ tab is a good place to start, and/or something that puts things related to challenges I posted and challenges I worked on.

A couple examples here

[mvexel]

@aawiseman I think you have something here and inbox organization is due for a bit of an overhaul. Tagging for discussion and inclusion in the next major version.