Add missing wysihtml5-0.3.0.js (closes #3)

Fetched from:
https://raw.github.com/xing/wysihtml5/master/dist/wysihtml5-0.3.0.js

Previously this file was imported through an SVN external.  We don't
currently have a great way of importing frontend dependencies of our PHP
scripts, and so we are including that file directly for now.