Move setup issue callout to under the header

Summary: Fixes T7830. Moves the callout to sit under the main header, which resolved Differential issues and Durable Column issues, but still some extra CSS shenanigans.

Test Plan:
Test lots of pages, Home, Dashboards, Conpherence, Durable Column, Inline Diff Replies, Mobile, Workboards, etc.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7830

Differential Revision: https://secure.phabricator.com/D12466