[communication] [position] Corrects some bugs the shared superBus files, as well as in the balise_principal and balise_mobile projects.  
* Fixes bugs in buffer reading/tests in lib_Xbee_arduino.cpp, adds payload checksum.
* Idem for lib_Xbee_x86.
* Little modification if the display of sniffer.
* Fixes the payload checksum computation.
* Fixes bug forwarding rules for Xbee subnet.
* Adds some debug message.
* Remark : compiles, but there is still a problem with payload reading in recepteur_laser.cpp.