Remove pro-white-background, re-style PHUIDocumentViewPro

Summary: This makes document views a little more automatic, and a little more style to the page. The Document itself remains on a pure white centered background, but footer and preceeding objects go back to the original body color. This provides a bit more depth and separation over content and definitions/comments.

Test Plan:
Tested Phriction, Diviner, Legalpad, Phame, Email Commands, HTTP Commands, with and without a footer.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14582