Load static resources via module descriptions

[altavir]

Some visualization features (like d3) require static or CDN resources like js, CSS, or images to be loaded into the current page. I think that the module descriptor JSON is the best place to describe such resources. I propose to add a resource (or static) block with a list of filenames or CDN paths to load when '%use' directive is invoked.

[ileasile]

This feature was added in the new library API and also supported in the old one