make differential use fluid width for code layout

Summary:
assume at least 360px for a given code pane. that's about when the comment box starts fighting back anyway. we'll use the yet-to-be-built one page render for the narrow viewport cases.

This address the cases as laid out in T2005. It fails the "MMMMM" case pretty horribly. However, if there is a space it works just fine and presumably folks are stretching out their windows on big glorious monitors at 160 characters wide or whatever.

Re-factored things just a tad but figure I'll take a nice big chunk of "renderer" to move forward T2009

Test Plan: looked at all sorts of funky diffs

Reviewers: epriestley

Reviewed By: epriestley

CC: chad, aran, Korvin

Maniphest Tasks: T2005

Differential Revision: https://secure.phabricator.com/D4083