Fix for bug #5691: link-element in html-body

To fix bug #5691 and produce valid HTML I have replaced the link-element in oepaypalexpresscheckoutminibasket.tpl by the smarty (plugin) function oxstyle. Probably this should be merged into b-3.0 and b-3.1, too?
I suppose that there are no unit-tests necessary for this change. ;) 
What about seleniums? Any changes needed there?