Client side PDF generation

@aaronjudd, I didn't publish the ongoworks:pdf package yet because I don't have permission. You can test the v0.2.2-pdf branch if you copy it locally though.

https://github.com/ongoworks/meteor-pdf

The generated PDF is pretty ugly, but I guess we can contribute to jsPDF to help them improve their HTML-to-PDF formatting.

I didn't remove the `createPDF` method or add a button on the admin orders page yet either. Wanted you to have a look first.