Summary: **WIP** This adds default capability to the Files application
Test Plan: Set default to public, go to Files page, see public preset. Upload File. Doesn't work.
Reviewers: btrahan, epriestley
Reviewed By: epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T6564
Differential Revision: https://secure.phabricator.com/D10888
