Phriction Redesign

Summary: This is mostly minor, but visually it makes the wiki feel more 'page like' and better separates the actual content from other data displayed.

Test Plan: Tested Chrome, iPhone, and iPad.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin, AnhNhan

Maniphest Tasks: T2686

Differential Revision: https://secure.phabricator.com/D5366