[communication] Modifies the debug message usage.
* Changes the debug payload type in messages.h to a pure string.
* Changes the way debug messages are entered : either a simple string (sb_printDbg), either a printf-like format command (sb_printfDbg).
* Changes the way the debug address is handled : it is now stored in a variable that can be updated by letting the debug console send a debug signalling message and feeding that message into sb_debugAddrSignal.