Optimizing aggregation and fixing bug in staff team listing route.
Optimizing aggregation and fixing bug in staff team listing route.

 - In `server/router/routes/staffTeamList.js` a match was needed in order to restrict the aggregation only to users with `role` equal to `volunteer`.

 - Optimizes aggregation calls for each request by caching the match and group query objects passed in.

AuburnBigEvent/BigEvent