Conpherence - us JX.Scrollbar in main conpherence view

Summary: Fixes T7681. Relatively straight forward since we don't "destroy" the main div the scroll bar is attached to, and instead just update the interior content.

Test Plan: played with conpherence in main view and scrolling never broke

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7681

Differential Revision: https://secure.phabricator.com/D12396