Clean up minor form spacing

Summary: Drops the inset box shadow and bumps standard UI elements from 28px to 30px. more room for activities.

Test Plan:
Spaces, Editing tasks, typeaheads, mobile, desktop.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D17660