Add Generators for Javascript Code.

Generators create javascript code that relays the responsibility of the
true ajax call onto a javascript function whose name the generator takes
as a parameter. It's up to the construction of the web app to make sure
that the function thus named is available for execution upon the calling
of proxy methods.

It is made this way so that the generators do not rely on any specific
framework (such as jQuery), and the code needed to be implemented by
application developers is only a small shim. Later versions will provide
at least the implementation under jQuery, which is currently the
recommended framework for use in Demoiselle Rest projects.