Add Disqus, Facebook, Google, GitHub auth config; AWS config
Summary: Also improve behavior for the "unknown config" warning.
Test Plan: Looked at configs, went through unknown config workflow.
Reviewers: btrahan, codeblock
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T2255
Differential Revision: https://secure.phabricator.com/D4310