plugins: styling fixes
 * remove archive.org plugin styling from main CSS, use icon instead
 * match archiveorg/readityourself plugins styling with qrcode
 * Icon from http://p.yusukekamiyamane.com/icons/search/fugue/icons/clock-history-frame.png under CC-BY-SA License
 * Icon from http://p.yusukekamiyamane.com/icons/search/fugue/icons/book-open.png under CC-BY-SA License