Clean up AphrontError boxes, Diffusion Headers

Summary: Two basic changes here, first we fixed up the Diffusion headers to roll out more PHUIObjectBoxes. Second we added some specific styles for when Errors are inside an ObjectBox at the first position.

Test Plan: Tested a number of different layouts for browsing respositories as well as wherever I could find cases with PHUIObjectBox Form Errors (see images attached). Still some minor tightening due after this diff, but didnt want to overload it.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D7914