Add "device ready" flag to standalone dialog pages
Summary: Fixes T5541. Standalone dialog pages, including the high-security auth page, should all work fine on mobile.
Test Plan:
Reviewers: chad, joshuaspence
Reviewed By: joshuaspence
Subscribers: epriestley
Maniphest Tasks: T5541
Differential Revision: https://secure.phabricator.com/D9799