Button to ignore setup issues + refractoring

Summary: T2381

Test Plan:
Click on the ignore link in /config/issue/ and respond to the dialog box.

Also, test uninstalling and reinstalling an application in the web UI (to verify that refractoring didn't break anything).

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2381

Differential Revision: https://secure.phabricator.com/D5234