Built in proxy for Mac (and parts for Linux)

Okay, second attempt with built in iOS proxy after some collaboration with @past (thanks!).

It now works well on first try for at least myself and @captainbrosset on Mac. More confirmation might be nice to have before merging.

Linux is coming along, but will likely need more changes.

Known issues on Linux
* On Ubuntu 12.04, I get "Could not connect to lockdownd"
* @past gets the same error

Known issues on Mac
* @past gets "Please verify that Settings > Safari > Advanced > Web Inspector = ON" error