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 Suggest to modify this line as follows:

```javascript
document.body.innerHTML = "";
document.body.append( contents );
```

This will ensure that all bound events and data will remain attached to the element instead of "flattening" it to just HTML string