Cache counts of edits and flags for faster reporting #52
Description
The curator report for item edits grouped by druid is slow, since you need to group by druid across the entire table before you can count the number of edits per druid and then sort by that. The only way I can think of to speed up this report is to pre-cache the number of edits per druid in some table (probably Item), so that each time an edit is made, it is incremented. You can then use this for sorting and counting instead of having to do a full table scan.
We should also do the same thing for edits by user and flags by user (cache edits/flags per user in the user table), including counts for flags by status, so you can easily obtain counts in each flag state (and sort by them) without having to join the flag table and re-compute counts by user each time.