Fix Dajax object visibility issue

[Kami]

Problem Description

Currently Dajax object is not attach to the window object. This means it won't be visible to other code (ReferenceError: Dajax is not defined) if you use a minification process which wraps all of the minified files inside a closure (function(){}())).

Most of the minification libraries, including commonly used django-pipeline do that.

Proposed solution

In my proposed solution, I've wrap Dajax object into a closure and attach it to the window object. I've also did some cleanup and changed the code to consistently use $ everywhere instead of using jQuery in some and $ in other places.

Attaching an object to window object is a fairly common thing to do if the code, like this one, is not built as a jQuery plugin.

[Kami]

@jorgebastida Would appreciate if you can have a look. Thanks!

[saz]

I've released my fork on pypi: https://pypi.python.org/pypi/django-dajax-ng