Missing isUS key

[indigo-jay]

It appears that at some point, isUS was added to the device config. Problem is, when accessing that key in the RFX library, they assume that it exists by referencing that key in the property dict. This fails for older devices that never had that key added. I think the best option would be to assume it's US (so do a .get("isUS", True)) and perhaps log the assumption and prompt the user to update the device. But there are other options as well (i.e. deviceStartComm could be updated to look for the missing key and do something there).