Add padding to last conpherenced-edited

Summary: In cases where conpherence-edited is the last item in the pane, we should add padding.

Test Plan: Enter a Room, edit the title, see extra padding. Submit a new comment, padding returns to default.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D12192