Require a CSRF code for Twitter and JIRA (OAuth 1) logins

Summary:
OAuth1 doesn't have anything like the `state` parameter, and I overlooked that we need to shove one in there somewhere. Append it to the callback URI. This functions like `state` in OAuth2.

Without this, an attacker can trick a user into logging into Phabricator with an account the attacker controls.

Test Plan:
  - Logged in with JIRA.
  - Logged in with Twitter.
  - Logged in with Facebook (an OAuth2 provider).
  - Linked a Twitter account.
  - Linked a Facebook account.
  - Jiggered codes in URIs and verified that I got the exceptions I expected.

Reviewers: btrahan, arice

Reviewed By: arice

CC: arice, chad, aran

Differential Revision: https://secure.phabricator.com/D8318