Bug 7584 - Update cart and lists buttons style using CSS3 features

Bug 7584 - Update cart and lists buttons style using CSS3 features

Replacing styling of cart and lists buttons with CSS3 features:
border-radius, background-gradient, multiple backgrounds. While
the CSS is a little more complicated, the markup is much simpler
which should make customization simpler.

Browsers tested:

Firefox 10 on Windows 7
Chrome 17 on Windows 7
Opera 11 on Windows 7
Internet Explorer 8 on Windows 7 (no rounded corners or background images)

Firefox 9 on Ubuntu 11.10
Chrome 16 on Ubuntu 11.10
Opera 11 on Ubuntu 11.10

Internet Explorer 6 on Windows XP (looks acceptably bad)

Signed-off-by: Nicole C. Engard <nengard@bywatersolutions.com>
Also tested in:

Safari on Mac OS X
Firefox 10 on Mac OS X
Chrome on Mac OS X

All the above tests passed

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>