correct array indices / size

std::fill(&Key2Event[0][0], &Key2Event[MAX_MODE][MAX_KEY], 0) is wrong
std::fill(&Key2Event[0][0], &Key2Event[MAX_MODE-1][MAX_KEY-1], 0) looks better but is still wrong
std::fill(&Key2Event[0][0], &Key2Event[MAX_MODE][MAX_KEY-1], 0) is also wrong
std::fill(&Key2Event[0][0], &Key2Event[MAX_MODE-1][MAX_KEY], 0) is correct but looks weird ;-)
Airspaces: add Serial attribute