[NRRPLT-2885] Added grey material to assets

Change-Id: If10e532a759c87baca4622e8649d0c126476c336

http/client/assets/materials/grey.material

+material Gazebo/Grey
+{
+  technique
+  {
+    pass main
+    {
+      ambient .3 .3 .3  1.0
+      diffuse .7 .7 .7  1.0
+      specular 0.01 0.01 0.01 1.000000 1.500000
+    }
+  }
+}