Feature Request: Team/User panel of challenges *not* completed. #74

Is your feature request related to a problem? Please describe.
When people are nearing the completion of the CTF, they usually have a lots of challenges finished. However it may be of interest to admins to find out which challenges were not solved.

Describe the solution you'd like
If we look at the current UI, we can see there is a "Solves" tab, and a "Stats" tab.

I'd like there to be a "Remaining" or "Unsolved" tab as well.

Describe alternatives you've considered
N(A

Additional context
N/A