Refactored ExportSystem to:
- Only fetch message counts once (instead of a query per member)
- Fetch switches using the newly refactored GetTruncatedSwitchList (gets switches and their members in one shot instead of querying for switch members one switch at a time)
- Added a new MessageCountsPerMember method to MemberStore to support the above
- Modified GetTruncatedSwitchList query to retrieve switches with no members (wasn't important for frontpercent, but is if we're reusing that method here)
This doesn't require any index changes beyond those that support GetTruncatedSwitchList, though we can see a small benefit with an index on messages covering the member column (valuable for other reasons outside of these additions).
adea7be07c