First go at implementing JSON output handlers.
Adding JS Plugins to enable people to include custom JS easily.
Adding comment about JS plugins.
Use os.walk to find all .js and .css files anywhere in jsplugins.
Handling JSON first and fixing when it is rendered for pyout.
Set include order of Notebook jsplugins.

Files are included in alphanumeric order of their full path, which may be used to ensure that javascript dependencies are met.

For example, given a.js depending on b.js:

jsplugins/0/b/b.js
jsplugins/1/a/a.js

ensures that a is included before b.