add ace's JavaScript webworker

this is kind of a monster at 10kloc, so we'll see if it causes
problems, but it enables cool stuff like jshint in assets

and we were getting console errors without it, so if we don't
want it, we should explicitly disable it

https://github.com/ajaxorg/ace/wiki/Syntax-validation
http://stackoverflow.com/questions/12886857/how-can-i-disable-the-syntax-checker-in-ace-editor