Use a more compatible script loading technique

Use `insertBefore` instead of `appendChild` to load JavaScript from the build service, like all most popular script loaders do (Google Analytics, Twitter widgets, Facebook like button, Disqus comments…).

Also puts it into a self executing anonymous function, which should be much safer than having it in the global scope.

/cc @triblondon 

![ ](http://gifs.joelglovier.com/hubbers/hubmojis-furyus-wink.gif)