Common Colors, Spacing for Menus and Typeaheads

Summary: Adds more consistent colors and spacing to notifications, conpherence dropdowns, search dropdowns, and typeaheads.

Test Plan: Tested Notifications, menu and page. Conpherence, menu and page, Search, and Typeaheads.

Reviewers: epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9313