Render the diff change index from JS instead of Django.
The new change index was about half template half javascript--we'd render the

basic table with each of the files from a django template, and then as diffs

were loaded, update it.
This change moves the initial render into the javascript as well. The data is

plumbed into javascript by passing it into the DiffViewerPageView. This change

is one step towards being able to update the displayed diff (revision/page/etc)

without reloading everything.

Viewed a handful of diff revisions and interdiffs. Saw the table as before in

  each case.
Ran js-tests
Ran jshint