Summary: Ref T3687. Depends on D6864. Implements the `OAuth1` provider in Phabricator (which is mostly similar to the OAuth2 provider, but doesn't share quite enough code to actually extend a common base class, I think) and Twitter as a concrete subclass.
Test Plan:
Created a Twitter provider. Registered, logged in, linked, refreshed account link.
{F57054}
{F57056}
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T3687
Differential Revision: https://secure.phabricator.com/D6865
