Fix Durable Column CSS-Overload

Summary: This moves the count on the Conpherence Menu Item into a phui-list-item-count, and removes the CSS call to the entire Conphrence stack when durable column is open.

Test Plan: Test with and without the chat column, and a menu with a count

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D17677