Make code blocks clear floats in Phriction
Summary: In situations where a code block and a ToC are displayed, this clears the float so the code block is always 100% wide.
Test Plan: Tested a code block with a ToC, iOS and Chrome
Reviewers: epriestley, btrahan
Reviewed By: epriestley
CC: aran, Korvin
Differential Revision: https://secure.phabricator.com/D6004