Allow admins to see list of requirement-meeting users

[orenyk]

Suggested by BYU:

It would be great to have the ability to create a report of who qualifies for each requirement. Maybe have the ability to search or sort in the user pane by requirement.

This should be almost trivial to implement, at least as a link on each requirements page (e.g. /requirements/:id/users). Adding the information to the Users table and sorting with it might be a bit trickier though.