improve racecar visuals a little bit with a texture on the wheels

data/racecar/meshes/hokuyo.mtl

@@ -0,0 +1,20 @@
+# Blender MTL File: 'None'
+# Material Count: 2
+
+newmtl black-material
+Ns 21.568627
+Ka 0.000000 0.000000 0.000000
+Kd 0.016250 0.016250 0.016250
+Ks 0.125000 0.125000 0.125000
+Ni 1.000000
+d 1.000000
+illum 2
+
+newmtl white_001-material
+Ns -1.960784
+Ka 0.000000 0.000000 0.000000
+Kd 0.556090 0.556090 0.556090
+Ks 0.031250 0.031250 0.031250
+Ni 1.000000
+d 1.000000
+illum 2