New ajax loader icon for Extension Manager

Scope: Replace ajax-loader.gif in media/jui/img/ with new, nicer looking "spinning all together" icon.

Why: The Joomla community is definitely stepping up it's game when it comes to the overall user experience, but there are a few things that still nag at my design sensibilities, and one of them is the Ajax Loader GIF Joomla uses when installing a new extension. While the existing animation is a positive step in the right direction, I think that we can do better.

To that end, I've designed an alternate Ajax Loader GIF to replace the one found in media/jui/img/ that I think aligns better with Joomla's branding and is just more pleasing to look at. I've already tried it out in some of my Joomla 3.3 installs and I must say it gives me a little goofy happy feeling every time I see it in the Extension Manager. I hope you'll enjoy it as well.

It's a very minor change, but with UX the Devil's in the details.