Fix super long topics in Conpherence header
Summary: Add some ellipsis if the topic is absurdly long.
Test Plan: desktop, mobile, tablet. MMMMMMMmmmMMMMMMmMMMmMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
Reviewers: epriestley
Reviewed By: epriestley
Subscribers: Korvin
Differential Revision: https://secure.phabricator.com/D16718