Add javascripts option to Editor constructor

Provide a way for users to add javascript files into iframe. 

Why? This came from a particular case: we use typekit. An it has to be loaded using a JS file. Hence, the improvement.

Also, in this PR is an up to date build of dist/wysihtml5-0.4.0pre.js and dist/wysihtml5-0.4.0pre.min.js