Initialization improvement: Inferring home location

[MikeBishop]

Currently, we assume that "home" is wherever the first car on the account is located when TWCManager starts up for the first time. That's not strictly correct, and some people have to recover from that. A stronger signal, if the TWC supports getting the VIN, is the current location of the first VIN reported by a slave. That would mean that we don't have a home location until a car is actually connected to the TWC, but that seems acceptable.