Added ability to set circuit state

This allows for, for example, turning on a water feature or changing pool/spa active status.

messages/SLSetCircuitStateMessage.js

@@ -0,0 +1,25 @@
+const SLMessage = require('./SLMessage.js').SLMessage;
+
+const MSG_ID = 12530;
+
+exports.SLSetCircuitStateMessage = class SLSetCircuitStateMessage extends SLMessage {
+  constructor(controllerId, circuitId, circuitState) {
+  	super(0, MSG_ID);
+
+  	this.controllerId = controllerId;
+  	this.circuitId = circuitId;
+  	this.circuitState = circuitState;
+  }
+
+  encode() {
+    this.writeInt32LE(this.controllerId || 0);
+    this.writeInt32LE(this.circuitId || 0);
+    this.writeInt32LE(this.circuitState || 0);
+
+    super.encode();
+  }
+
+  static getResponseId() {
+    return MSG_ID + 1;
+  }
+}