Color tweaks for action list, headers

Summary: Starting to roll out the standard colors and spacing to action list, headers, and property views. Also softened the grey borders a hex.

Test Plan: Review Maniphest and Differential on desktop and mobile. Felt the flow of standardization waft over me.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: Korvin, aran

Differential Revision: https://secure.phabricator.com/D6869