add support for commercial wifi connection prompts

[bonds]

At some places, like airports and cafes, when you first try to surf the web, they hijack your web session and direct you to a website where you must accept their terms before you can connect to the outside world.

At present, this does not play well with PF rules that disallow traffic except through VPN.

[bonds]

https://en.wikipedia.org/wiki/Captive_portal

[bonds]

http://apple.stackexchange.com/questions/45418/how-to-automatically-login-to-captive-portals-on-os-x

[bonds]

https://github.com/Tyilo/NetworkAutoLogin