Add Universal Analytics (bug 1018934)

~~We need to add some ability to merge settings with settings provided via the page like we currently do in webpay. That can likely be done as a separate thing though.~~ See: #73
Apparently there's a ton of compat issues: https://github.com/Modernizr/Modernizr/blob/master/feature-detects/storage/localstorage.js (whilst they might not all apply, this seemed simple enough and more likely to not blow-up).