[Mesh] Captive Portal Garden Gnome

Hey folks, I enabled the "garden gnome" on the production exit server. What this should do is trigger certain operating system's network connectivity probes so that they'll show a splash page when people join the network. It's designed to be as minimally intrusive as possible, so it only captures probes to the specific urls that OSX/iOS/Android/Windows test to see if they're connected to the internet. Once a user clicks "go to the internet", that IP will be added to a white list so they won't see the splash page again for 24 hours. Please please please let me know if there are any issues that you encounter. We absolutely don't want to have people unable to connect to the network for some reason or another. I don't really have enough devices to test on, so it's very possible that there could be an issue somewhere. There are a couple design bits that I know I need to polish, but I'm open to constructive feedback on any aspect of it. Thanks! Maxb