Use standard UI elements to render pull requests in Releeph

Summary:
Ref T3718. Ref T3644. Ref T3092. Switches from the Releeph UI elements to standard ones. I'll attach some screenshots.

Also fixes CSRF against the request action endpoint.

Test Plan:
  - Viewed request details.
  - Took actions on a request from detail page.
  - Viewed request list.
  - Took actions on a request from list page.
  - Used keyboard shortcuts to navigate list.
  - Used keyboard shortcuts to take actions.
  - Simulated errors.
  - Viewed on devices.

Reviewers: chad, btrahan

Reviewed By: btrahan

Subscribers: grp, FacebookPOC, mattlqx, tala, beng, LegNeato, epriestley

Maniphest Tasks: T3718, T3092, T3644

Differential Revision: https://secure.phabricator.com/D8771