Added example sketch for a secure actuator

The sketch closely resembles the RelayActuator example.
The difference is that this sketch require gateway to sign
all messages addressed to the actuator.

libraries/MySensors/examples/SecureActuator/SecureActuator.ino

@@ -0,0 +1,57 @@
+// Example sketch showing how to securely control locks. 
+// This example will remember lock state even after power failure.
+
+#include <MySensor.h>
+#include <SPI.h>
+
+#ifndef MYSENSORS_SENSOR
+#error Please switch to MYSENSORS_SENSOR in MyConfig.h
+#endif
+
+#define LOCK_1  3  // Arduino Digital I/O pin number for first lock (second on pin+1 etc)
+#define NOF_LOCKS 1 // Total number of attached locks
+#define LOCK_LOCK 1  // GPIO value to write to lock attached lock
+#define LOCK_UNLOCK 0 // GPIO value to write to unlock attached lock
+
+MySensor gw;
+
+void setup()  
+{   
+  // Initialize library and add callback for incoming messages (signing is required)
+  gw.begin(incomingMessage, AUTO, true, AUTO, true);
+  // Send the sketch version information to the gateway and Controller
+  gw.sendSketchInfo("Secure Lock", "1.0");
+
+  // Fetch lock status
+  for (int lock=1, pin=LOCK_1; lock<=NOF_LOCKS;lock++, pin++) {
+    // Register all locks to gw (they will be created as child devices)
+    gw.present(lock, S_LOCK, false);
+    // Then set lock pins in output mode
+    pinMode(pin, OUTPUT);   
+    // Set lock to last known state (using eeprom storage) 
+    digitalWrite(pin, gw.loadState(lock)?LOCK_LOCK:LOCK_UNLOCK);
+  }
+}
+
+
+void loop() 
+{
+  // Alway process incoming messages whenever possible
+  gw.process();
+}
+
+void incomingMessage(const MyMessage &message) {
+  // We only expect one type of message from controller. But we better check anyway.
+  if (message.type==V_LOCK_STATUS && message.sensor<=NOF_LOCKS) {
+     // Change relay state
+     digitalWrite(message.sensor-1+LOCK_1, message.getBool()?LOCK_LOCK:LOCK_UNLOCK);
+     // Store state in eeprom
+     gw.saveState(message.sensor, message.getBool());
+     // Write some debug info
+     Serial.print("Incoming change for lock:");
+     Serial.print(message.sensor);
+     Serial.print(", New status: ");
+     Serial.println(message.getBool());
+   } 
+}
+