add orthographic toggle and mesh cycling to prepare for branch to core_3d_camera_view simplification

examples/core/resources/models/unit_cube.obj

@@ -0,0 +1,22 @@
+o unit_cube
+v -0.5 -0.5 -0.5
+v  0.5 -0.5 -0.5
+v  0.5  0.5 -0.5
+v -0.5  0.5 -0.5
+v -0.5 -0.5  0.5
+v  0.5 -0.5  0.5
+v  0.5  0.5  0.5
+v -0.5  0.5  0.5
+s off
+f 1 4 3
+f 1 3 2
+f 5 6 7
+f 5 7 8
+f 1 5 8
+f 1 8 4
+f 2 3 7
+f 2 7 6
+f 4 8 7
+f 4 7 3
+f 1 2 6
+f 1 6 5