Bootloader: Add support for couplers #74
Description
At the moment, the Bootloader always uses address 15.15.192, which is incompatible with couplers as that address is surely not in their routing table.
To solve this, the PC Updater should send an A_IndividualAddress_Write to assign the Bootloader the physical address of the device it is on, and use that address for all further communication.