Investigate use of XBee Series 3 devices

[NameOfTheDragon]

During development of release 3.0.0, XBee Series 3 devices were tried and found not to be 100% backward compatible with the XBee Series 1 devices. Although they are pin-compatible and the API is very similar, there are some minor differences and the firmware as currently designed will not work with them.

XBee series 1 has been discontinued by the manufacturer and although they are still available, clearly this is not going to hold true forever and we will need to move over to the XBee series 3 devices.

@nexdome has requested that @NameOfTheDragon investigates what changes would be needed to make the firmware compatible with both S1 and S3 XBees.