Extract DOM push.js transitions
**Summary:** Ratchet's view transitions (push.js) are a key for emulating the experience of a native mobile app, but they're tightly coupled with the PJAX approach to loading new content.

**Problem:** This is a major blocker for developers who want to render then display content on the client without a PJAX request (e.g. client side rendering with Backbone).

**Proposed Solution:** Separate the PJAX (AJAX, request caching & click/touch binding) and DOM transition responsibilities of [push.js](https://github.com/twbs/ratchet/blob/master/js/push.js) into two different files. Then expose a new function (like `PUSH`) that allows DOM replacement/transitions without retrieving new content via an AJAX request.

I've hacked together a solution for my own use, but I'd like to polish it and submit it as a pull request if the maintainers are interested. /cc @connors 
