Update Form Layouts

Summary:
This attempts some consistency in form layouts. Notably, they all now contain headers and are 16px off the sides and tops of pages. Also updated dialogs to the same look and feel. I think I got 98% of forms with this pass, but it's likely I missed some buried somewhere.

TODO: will take another pass as consolidating these colors and new gradients in another diff.

Test Plan: Played in my sandbox all week. Please play with it too and let me know how they feel.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: Korvin, aran

Differential Revision: https://secure.phabricator.com/D6806