enable planar reflection in MinitaurGymEnv

enable follow cam in other Gym locomotion environments
add testing assets for multi-material obj files -> sdf conversion.
Also use ER_NO_SEGMENTATION_MASK flag for TinyRenderer/EGL plugin renderer

data/threecubes/part2.obj

@@ -0,0 +1,60 @@
+# Exported using automatic converter by Erwin Coumans
+mtllib three_cubes.mtl
+#object Cube
+
+v -4.474365 4.513343 2.535691
+v -4.474365 2.513344 2.535691
+v -4.474365 2.513343 4.535690
+v -2.474365 4.513343 2.535691
+v -2.474365 2.513344 2.535691
+v -4.474365 2.513344 2.535691
+v -2.474365 4.513343 4.535691
+v -2.474365 2.513343 4.535690
+v -2.474365 2.513344 2.535691
+v -4.474365 4.513343 4.535691
+v -4.474365 2.513343 4.535690
+v -2.474365 2.513343 4.535690
+v -4.474365 2.513344 2.535691
+v -2.474365 4.513343 4.535691
+v -2.474365 4.513343 2.535691
+v -4.474365 4.513343 4.535691
+v -4.474365 4.513343 2.535691
+v -2.474365 4.513343 2.535691
+v -2.474365 4.513343 4.535691
+v -4.474365 2.513343 4.535690
+usemtl Material
+
+
+vt 1.000000 0.000000
+vt 1.000000 1.000000
+vt 0.000000 1.000000
+vt 1.000000 0.000000
+vt 1.000000 1.000000
+vt 0.000000 1.000000
+vt 1.000000 0.000000
+vt 1.000000 1.000000
+vt 0.000000 1.000000
+vt 1.000000 0.000000
+vt 1.000000 1.000000
+vt 0.000000 1.000000
+vt 1.000000 0.000000
+vt 1.000000 1.000000
+vt 0.000000 1.000000
+vt 0.000000 0.000000
+vt 0.000000 0.000000
+vt 0.000000 0.000000
+vt 0.000000 0.000000
+vt 0.000000 0.000000
+s off
+f 1/1/1 2/2/2 3/3/3
+f 4/4/4 5/5/5 6/6/6
+f 7/7/7 8/8/8 9/9/9
+f 10/10/10 11/11/11 12/12/12
+f 13/13/13 5/5/5 12/12/12
+f 10/10/10 14/14/14 15/15/15
+f 16/16/16 1/1/1 3/3/3
+f 17/17/17 4/4/4 6/6/6
+f 18/18/18 7/7/7 9/9/9
+f 19/19/19 10/10/10 12/12/12
+f 20/20/20 13/13/13 12/12/12
+f 17/17/17 10/10/10 15/15/15