Efficient querying of tabular view data

In the currently checked in version of the tabular view coach reports, we make a database query per user to get data out.

Changes:
* Only query once (for all users)

Notes:
* On my local machine with 20 users, this reduced queries from 35 to 16 (of course), from 50ms in SQL to 22ms, and from 420ms overall to ~260ms (all numbers via the Django Debug Toolbar