Provides access to third party Javascript libraries in clojupyter.

Replaces `clojupyter.misc.helpter/add-javascript` which is
deprecated because Jupyter no longer allows arbitrary `script` tags
to be sent by kernels but instead supports libraries loaded using
RequireJS (cf. https://requirejs.org) an implementation of
Javascript Asynchronuous Module Definitions (AMDs).

Alpha version - breakage may happen.  Please report issues or
missing features.