by Gina Trapani Photo-sharing web application Flickr is like an onion: it has many, many layers to discover. Last February I published an article here on Lifehacker called Tips for Flickr beginners, a quick rundown on how to get started on Flickr. One year later I'm still as big a Flickr fan and user as ever, so it's about time to point out some of the more advanced features of the amazing, ever-e