R1:b2c23d88e8f9

Implement HTTP response messages

Summary: Fixes T7486. Implement HTTP response messages such as `200 OK` and `404 Not Found`. The status codes were taken from http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html.

Test Plan: Navigated to `/foo` and saw the response showing `404 Not Found` in the Network tab of Chrome.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7486

Differential Revision: https://secure.