Added printing sample.

Hi Renato/Joe,

This is a sample that uses window.print() that I'd like to include to demonstrate how to print using Chrome apps.

I don't have write access to the repository, and would appreciate your review of this sample in any case. Can you review & pull if appropriate. I can implement any suggestions you have in the fork or set up permissions appropriately and do it in the master.

    - Charles (a.k.a. dharcourt@)