Add support for setting the current system date/time

#56

messages/SLSetSystemTime.js

@@ -0,0 +1,28 @@
+'use strict';
+
+const SLMessage = require('./SLMessage.js').SLMessage;
+
+const MSG_ID = 8112;
+
+exports.SLSetSystemTime = class SLSetSystemTime extends SLMessage {
+  constructor(buf, date, shouldAdjustForDST, senderId) {
+    if (buf) {
+      var size = buf.readInt32LE(4) + 8;
+      super(buf, MSG_ID, size);
+    } else {
+      super(senderId, MSG_ID);
+
+      this.date = date;
+      this.shouldAdjustForDST = shouldAdjustForDST;
+    }
+  }
+
+  encode() {
+    this.writeSLDateTime(this.date);
+    this.writeInt32LE(this.shouldAdjustForDST ? 1 : 0);
+  }
+
+  static getResponseId() {
+    return MSG_ID + 1;
+  }
+};