Add audio onebox
http://meta.discourse.org/t/audio-html5-tag/8168
Merge branch 'add-audio-onebox' of git://github.com/jamesaanderson/discourse into jamesaanderson-add-audio-onebox

Conflicts:
	app/assets/stylesheets/application/compose.css.scss
	app/assets/stylesheets/application/topic-post.css.scss