re #428: Vomit JsMutationObserver into script tag in editor.php.

CKEditor build process assumed it should try to compile the
JavaScript file, which was breaking things rather badly.

This hopefully won't be necessary at all for much longer, because we
should be able to solve the same problem that MutationObserver is currently
being used to address with considerably fewer hacks once we have the
WIRIS server components.