Add PAI Bluetooth—private chat between PAI and its carrier 

[Forum thread](http://baystation12.net/forums/viewtopic.php?f=5&t=11348)

This branch adds an ability for PAI and PAI carriers (people with a PAI card in inventory) to converse using the ":p" prefix. These conversations require the carrier to be wearing a headset, and are explained as some sort of a personal area radio network, that allows the PAI to speak directly in the carrier's ear. From the outside, it looks like talking on radio, and from the inside it looks like a separate radio channel. 

There were some suggestion that there should be a way to eavesdrop on the conversations (other than by being a ghost), but I am holding off on that.