Quicksand - provide some plumbing for fancier updates

Summary: Ref D12448. Ref T7573. This changes quicksand up a bit so rather than caching just rendered HTML we also cache the initial response from the server. We also fire off a quicksand-redraw event which will let things like the page objects for notifications update correctly while using Quicksand (see D12448).

Test Plan: loaded up /p/btrahan/ Clicked the UI elements to navigate to various profile views up to maniphest. clicked back until back at /p/btrahan/ and it worked. clicked forward until all the way back to maniphest and it worked. clicked back 2x, then clicked new links, then back and it worked

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7573

Differential Revision: https://secure.phabricator.com/D12449