#6 Clock subsriber and ToolTime upgraded for ROS usage

Closes #6 (closed)

Assets/AddOns/RosSharp/Scripts/RosBridgeClient/RosCommuncation/ClockSubscriber.cs

+using UnityEngine;
+
+namespace RosSharp.RosBridgeClient
+{
+    public class ClockSubscriber : Subscriber<Messages.rosgraph_msgs.Clock>
+    {
+        private float deltaTime = 0;
+        private float lastTime = 0;
+
+        private uint secs = 0;
+        private uint nsecs = 0;
+
+        public float DeltaTime { get { 
+            float dt = deltaTime;
+            deltaTime = 0;
+            return dt;
+        }}
+
+		protected override void Start()
+		{
+			base.Start();
+		}
+		
+        protected override void ReceiveMessage(Messages.rosgraph_msgs.Clock message)
+        {
+            secs = message.clock.secs;
+            nsecs = message.clock.nsecs;
+            float currentTime = (float)(secs) + (float)(nsecs)/1e9f;
+            deltaTime = currentTime - lastTime;
+            lastTime = currentTime; 
+        }
+
+    }
+}