Summary: Ref T13249. Poll for Duo updates in the background so we can automatically update the UI when the user clicks the mobile phone app button.
Test Plan: Hit a Duo gate, clicked "Approve" in the mobile app, saw the UI update immediately.
Reviewers: amckinley
Reviewed By: amckinley
Maniphest Tasks: T13249
Differential Revision: https://secure.phabricator.com/D20169
