Expose Fondant class globally to allow for overrides as needed in app

Just a minor change to the architecture to allow `Fondant` to be accessible and extended outside of this file. 

Also, I moved the setup from within a `$(function() {});` to just work if jQuery is defined. This allows it to be accessible in the global scope.

Let me know what you think @philtr 

(Tests were already failing so I haven't touched those.)