Always reset scroll after durable column is maximized

Summary: When the durable column is re-opened, scroll user to latest message. Though later we should scroll them to the last read.

Test Plan: Minimize window, reload page, pop up window, see proper scroll position.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D16649