Updated the iTunes button CSS for a better position

The position was working fine the last time, I don't know what fucked it
up this time.
Improved the artwork link, now shows both x600 and x1200

For reasons I don't completely understand, the image source wasn't
returning what it should have.

So, I'm now using the other link.

Hacks Hacks Hacks!
The edit not now contains a link to the userscript

...on nikki's bitbucket
https://bitbucket.org/96187/userscripts/src/HEAD/itunes-importer/