add z-up version of Laikago, centered along the chassis center of mass

examples/pybullet/gym/pybullet_data/laikago/chassis_zup.mtl

@@ -0,0 +1,13 @@
+# Blender MTL File: 'None'
+# Material Count: 1
+
+newmtl None.003
+Ns 0.000000
+Ka 0.000000 0.000000 0.000000
+Kd 0.800000 0.800000 0.800000
+Ks 0.800000 0.800000 0.800000
+Ke 0.000000 0.000000 0.000000
+Ni 1.000000
+d 1.000000
+illum 2
+map_Kd laikago_tex.jpg