Theme updates 

Ant's theme updates:

> Mostly minor clean up and clarification. Shooting small critters for f.un. :D
> Should fix #539, #561, #567. Made a start on admin.css.
> GenericList.template, Memberlist.template and Search.template got some new stuff for styling rows.
> Memberlist.template.php had the posts bars removed (see https://github.com/elkarte/Elkarte/issues/620).
> index.template.php is mostly additions of some aria stuff for a11y and
> (wait for it)
> removal of html5 structural tags (also for a11y, believe it or not).