Make Pholio URIs aware of which image you are looking at

Summary: Fixes T2658. Map `/Mxx/yy/` to images in a mock. Use HTML5 history stuff to make it work nicely. This also makes right-click-open-in-new-tab work correctly.

Test Plan: Clicked thumbs in a mock. Right-clicked thumbs. Copy and pasted a URI. Used browser back button.

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T2658

Differential Revision: https://secure.phabricator.com/D5222