Theme Updates II

Apart from that, a fair bit of basic markup cleanup and some WAI-ARIA a11y tweaks. Divs where divs didn't need to be have been killed, with just nice clean ul's left. Name changes for better semantics. Large chunks of CSS have been moved around to try and get the ordering more sensible. Some other stuff.

Should address
#554
#550
#548
#517

Maybe some others