I was out to dinner with a couple of girlfriends from college recently when the conversation turned to Snapchat, the photo- and video-sharing app seemingly beloved by millennials and profoundly misunderstood by everyone else.  “I don’t get it,” my friend Anna confessed, as she Googled her way to a Quora page full of praise for Snapchat’s “social engagement loop”: “It may look like a toy but underneath the buzz is a beautifully designed app for personally connecting with friends.”  If you’re anything like me, you’ll need a little more convincing. In that case, check out our annual year-in-preview feature, “New & Next: 10 Hot Retail Topics for 2016,” which includes an item on Snapchat. The reason we believe the app belongs on a list of the top 10 things retailers need to know in the new year? That’s easy: It’s the fastest growing social netwo