Updated Thread.cpp|.h to support signal clear

[raulMrello]

Added functionality to clear consumed signal flags on thread waiting. Example of use:

Thread * _th;
// .....
// .....
// Waits for signal flag 1 or 2... 
for(;;){
  osEvent oe = _th->signal_wait((1 | 2), 0);
  if(oe.status == osEventSignal && (oe.value.signals & 1) != 0){
      _th->signal_clr(1);
     // add handling code for signal flag 1
  }
  if(oe.status == osEventSignal && (oe.value.signals & 2) != 0){
      _th->signal_clr(2);
     // add handling code for signal flag 2
  }

}