Add flag to invert DCC Accessory command <a> behaviour

<a addr subaddr 1> command puts a D=1 into the DCC packet for a DCC Accessory Decoder.  This was previously though to correspond to a 'throw' request and a D=0 to a 'close' request.  RCN-213 standard identifies that D=1 is 'close' and D=0 is 'throw', so this change allows CS to be configured to invert the states to conform to the RCN-213 definition.

DCC.cpp

@@ -239,6 +239,9 @@ void DCC::updateGroupflags(byte & flags, int16_t functionNumber) {
 }
 
 void DCC::setAccessory(int address, byte number, bool activate) {
+  #ifdef DIAG_IO
+  DIAG(F("DCC::setAccessory(%d,%d,%d)"), address, number, activate);
+  #endif
   // use masks to detect wrong values and do nothing
   if(address != (address & 511))
     return;