Allow non-pjax page updates.

Extract transition functionality from push.js into a new file, transitions.js.
Expose a global function, similar to PUSH named TRANSITION used to transition
from one page/view to another without dictating how the new markup is sourced.

This allows for Ratchet style page transitions when rendering client side.

I'll add comments to the diff shortly, highlighting some of the changes I've made.
@ndelage As below - using `.innerHTML` flattens the element to its HTML string thus removing any attached event listeners or references to this element. I suggest to use `.appendChild()` instead