RTL Support for version 2

Hello,

A while ago I've submitted RTL support for version 1.x, and when I read the blog post on developmentseed.org regarding version 2, I was very excited to give it a test drive. It turned out to be great, actually very great! so I made RTL css sheets, so I can use on my Arabic sites (I think Admins will be very happy).

I've made RTL files for Admin v2 and rubik, but there are few problems regarding images, like admin's sprite.png and rubik's sprite.png because there is only one arrow shape that is left arrow (arrow that points to left), where RTL UI needs right arrows so if you could modify these images and include right arrows it'll be great.

One more thing regarding div#admin-toolbar.nw span.admin-toggle class in admin.toolbar.css line 210, I think nw means north-west, anyhow in RTL UI the admin toolbar have to appear on the right so moving it to the right makes it's position ne (north-east) not nw, so the bad way is to modify nw background position to make like ne, and the right and better way is to make $position variable inside div#admin-toolbar's class RTL friendly.

Thanks for this great module and great release!