Backbone 1.0 tweaks

For https://github.com/afeld/backbone-nested/pull/96.

The model tests were being run in two different ways, so this consolidates them all into one test file.  The single entry point is also nice for only needing to open one page in the browser.

Worth noting that `test/model.js` was from Backbone 0.9.2, so that version works!  /cc https://github.com/afeld/backbone-nested/issues/100