add test box for mtl loader

Playground/scenes/Box/Box.mtl

@@ -0,0 +1,16 @@
+# 3ds Max Wavefront OBJ Exporter v0.97b - (c)2007 guruware
+# File Created: 29.06.2018 00:36:27
+
+newmtl 01___Default
+	Ns 10.0000
+	Ni 1.5000
+	d 1.0000
+	Tr 0.0000
+	Tf 1.0000 1.0000 1.0000 
+	illum 2
+	Ka 0.5882 0.5882 0.5882
+	Kd 0.5882 0.5882 0.5882
+	Ks 0.0000 0.0000 0.0000
+	Ke 0.0000 0.0000 0.0000
+	map_Ka 20140615_192225.png
+	map_Kd 20140615_192225.png

Playground/scenes/Box/Box.obj

@@ -0,0 +1,52 @@
+# 3ds Max Wavefront OBJ Exporter v0.97b - (c)2007 guruware
+# File Created: 29.06.2018 00:36:27
+
+mtllib Box.mtl
+
+#
+# object Box001
+#
+
+v  -13.8390 0.0000 16.0985
+v  -13.8390 0.0000 -16.1733
+v  13.2327 0.0000 -16.1733
+v  13.2327 0.0000 16.0985
+v  -13.8390 23.5656 16.0985
+v  13.2327 23.5656 16.0985
+v  13.2327 23.5656 -16.1733
+v  -13.8390 23.5656 -16.1733
+# 8 vertices
+
+vn -0.5774 -0.5774 0.5774
+vn -0.5774 -0.5774 -0.5774
+vn 0.5774 -0.5774 -0.5774
+vn 0.5774 -0.5774 0.5774
+vn -0.5774 0.5774 0.5774
+vn 0.5774 0.5774 0.5774
+vn 0.5774 0.5774 -0.5774
+vn -0.5774 0.5774 -0.5774
+# 8 vertex normals
+
+vt 1.0000 0.0000 0.0000
+vt 1.0000 1.0000 0.0000
+vt 0.0000 1.0000 0.0000
+vt 0.0000 0.0000 0.0000
+# 4 texture coords
+
+o Box001
+g Box001
+usemtl 01___Default
+s 2
+f 1/1/1 2/2/2 3/3/3 4/4/4 
+s 4
+f 5/4/5 6/1/6 7/2/7 8/3/8 
+s 8
+f 1/4/1 4/1/4 6/2/6 5/3/5 
+s 16
+f 4/4/4 3/1/3 7/2/7 6/3/6 
+s 32
+f 3/4/3 2/1/2 8/2/8 7/3/7 
+s 64
+f 2/4/2 1/1/1 5/2/5 8/3/8 
+# 6 polygons
+