Enhancements to Team Stats page

In #530 an initial version of Team Statistics was created. This issue is to document some likely improvements we could make.

The current implementation has some summary statistics and 2 main tables: Team Stats and Team Campaigns: The Team Stats table summarizes edits for all team members across all of time and all campaigns. The Team Campaigns table is simply a list of campaigns assigned to the team. The two tables are *not* linked views. Options for filtering or faceted search here, which could be added:

- filter by single campaign: show team stats only for the selected team campaign
- assigned campaigns only mode: show team stats for only the set of assigned campaigns
- all campaigns mode: show team stats and all campaigns which have activity for these team members, regardless of assignment.

Relates to #198 , #530