Import third-party libraries in livesketch examples via CDN

[SableRaf]

As mentioned in #314, some livesketch examples might require the use of third party libraries to emulate features of Processing that currently do not exist in p5.js

The suggested approach is to add an array of imports to the .json config file like so:

"import": ["https://cdnjs.cloudflare.com/ajax/libs/paper.js/0.12.15/paper-core.js"]