R1:9470ab057640

First go at Files settings.

Summary:
Based on @epriestley's https://secure.phabricator.com/differential/diff/9186/
plus others that seemed like they belong here.

Test Plan: Saw the new settings show up in the web interface.

Reviewers: epriestley, btrahan, chad

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2255

Differential Revision: https://secure.phabricator.com/D4425