Get rid of some IE6/7 specific code.

Make playlist panel collapsible.
Get rid of the nested divs/image files based rounded corners. Use CSS
border-radius instead.
Force redraw of the playlist panel when it's being expanded.
Merge branch 'public/7.9' into public/feature/webskin
Re-enable state of the collapsible panel. Need to tweak playtime
progressbar to make it not break if the page is loaded in collaped
state.
Merge branch 'public/7.9' into public/feature/webskin
Improve MSIE compatibility. Force it into IE9 mode. Enable panel state
management on MSIE, too.
Merge branch 'public/7.9' into public/feature/webskin
Merge branch 'public/feature/webskin' into public/7.9
Changelog update