Adding peptide cartoons / ribbons for Avo2

Dear Gaurav and Jonathan,

First off, thanks both for coming and giving great talks at the User Group Meeting a few weeks ago, and for Jonathan's pile of patches and pull requests.

It's great to see how Avo2 is helping out, and I think there's going to be continuing interest in "gamifying" force fields, etc.

You had mentioned during the meeting about cartoon and ribbon rendering, and that you liked the quality in Avogadro v1.x. Unfortunately, some of that code came from GPL codebases and we can't directly port it. So I'm curious how you feel about the cartoon rendering from 3Dmol.js:

David Koes is a colleague and collaborator and we know that code is BSD-licensed.