Increase Conpherence notification panel transaction fetch

Summary: We currently fetch 15 transactions for 5 rooms, which leads to some room subtitles in the notification panel to being blank since nothing was fetched. I don't think this is a great fix, but moves the bar much further. Maybe there is a more accurate fix that isn't 5 SQL queries?

Test Plan: Review notification panel in sandbox, ensure all threads have some additional information.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D16695