Allow authentication providers to store and customize additional configuration

Summary:
Ref T1536. None of this code is reachable.

For the new web UI for auth edits, give providers more and better customization options for handling the form. Allow them to format transactions.

Also fix the "Auth" application icon.

Test Plan: {F46718}

Reviewers: btrahan, chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T1536

Differential Revision: https://secure.phabricator.com/D6221