merging feature/multi image upload (without replacement of current image upload links)

The upload UI has been given some styling and x-browser testing. Design-wise it's ready for review. Back-end wise @sixpearls code is still to be reviewed by a django dev.

I've not replaced the current upload system with this yet due to IE9, which doesn't support most of this the new system and I'm yet to arrive at a satisfactory solution.

IE9 doesn't support the `X-Requested-With` header, meaning as the backend code stands, no files are ever uploaded because the  `if request.POST and request.is_ajax():` clause is false. Furthermore it has no support for the File API anyway, so progress indicators etc aren't supportable, which was the main benefit of this new upload system. tl;dr: it doesn't work at all in IE9.

My feeling is that getting it to all fall back nicely in IE9 is just too much work for too little benefit. I've become rather lost trying to figure out what would need to be done. I'd suggest we don't allow IE9 users to use this new upload system at all, redirecting them to the original instead. Users of IE9 will have `.lt-ie10` on the HTML tag which is easily detected and used as a basis for redirection either by meta tags or js.