Add model[] formspec element (#10320)

Formspec element to display models, written by @kilbith, rebased and tweaked.

Co-authored-by: Jean-Patrick Guerrero <jeanpatrick.guerrero@gmail.com>
Co-authored-by: sfan5 <sfan5@live.de>

games/devtest/mods/testformspec/LICENSE.txt

@@ -0,0 +1,14 @@
+License of media files
+----------------------
+Content imported from minetest_game.
+
+
+BlockMen (CC BY-SA 3.0)
+  default_chest_front.png
+  default_chest_lock.png
+  default_chest_side.png
+  default_chest_top.png
+
+stujones11 (CC BY-SA 3.0)
+An0n3m0us (CC BY-SA 3.0)
+  testformspec_character.b3d

games/devtest/mods/testformspec/formspec.lua

@@ -327,6 +327,10 @@ Number]
 			animated_image[3,4.25;1,1;;testformspec_animation.png;4;0;3]
 			animated_image[5.5,0.5;5,2;;testformspec_animation.png;4;100]
 			animated_image[5.5,2.75;5,2;;testformspec_animation.jpg;4;100]
+
+			style[m1;bgcolor=black]
+			model[0.5,6;4,4;m1;testformspec_character.b3d;testformspec_character.png]
+			model[5,6;4,4;m2;testformspec_chest.obj;default_chest_top.png,default_chest_top.png,default_chest_side.png,default_chest_side.png,default_chest_front.png,default_chest_inside.png;30,1;true;true]
 		]],
 
 	-- Scroll containers

games/devtest/mods/testformspec/models/testformspec_chest.obj

@@ -0,0 +1,79 @@
+# Blender v2.78 (sub 0) OBJ File: 'chest-open.blend'
+# www.blender.org
+o Top_Cube.002_None_Top_Cube.002_None_bottom
+v -0.500000 0.408471 0.720970
+v -0.500000 1.115578 0.013863
+v -0.500000 0.894607 -0.207108
+v -0.500000 0.187501 0.499999
+v 0.500000 1.115578 0.013863
+v 0.500000 0.408471 0.720970
+v 0.500000 0.187501 0.499999
+v 0.500000 0.894607 -0.207108
+v -0.500000 0.187500 -0.500000
+v -0.500000 -0.500000 -0.500000
+v -0.500000 -0.500000 0.500000
+v 0.500000 0.187500 -0.500000
+v 0.500000 -0.500000 0.500000
+v 0.500000 -0.500000 -0.500000
+vt 0.0000 1.0000
+vt 0.0000 0.0000
+vt 1.0000 0.0000
+vt 1.0000 1.0000
+vt 1.0000 0.0000
+vt 1.0000 1.0000
+vt 0.0000 1.0000
+vt 0.0000 0.0000
+vt 0.0000 1.0000
+vt 1.0000 1.0000
+vt 1.0000 0.6875
+vt 0.0000 0.6875
+vt 1.0000 1.0000
+vt 0.0000 0.6875
+vt 1.0000 0.6875
+vt 1.0000 0.6875
+vt 1.0000 0.0000
+vt 0.0000 0.0000
+vt 1.0000 0.6875
+vt 1.0000 0.0000
+vt 1.0000 1.0000
+vt 1.0000 0.6875
+vt 1.0000 0.0000
+vt 0.0000 1.0000
+vt 0.0000 0.6875
+vt 0.0000 0.6875
+vt 0.0000 0.0000
+vt 1.0000 0.5000
+vt 1.0000 1.0000
+vt 0.0000 1.0000
+vt 0.0000 0.5000
+vt 0.0000 0.0000
+vt 1.0000 0.0000
+vn 0.0000 0.7071 0.7071
+vn -0.0000 -1.0000 -0.0000
+vn -1.0000 0.0000 0.0000
+vn 1.0000 0.0000 -0.0000
+vn 0.0000 -0.7071 0.7071
+vn 0.0000 0.0000 1.0000
+vn -0.0000 0.7071 -0.7071
+vn -0.0000 0.0000 -1.0000
+vn -0.0000 -0.7071 -0.7071
+vn -0.0000 1.0000 -0.0000
+g Top_Cube.002_None_Top_Cube.002_None_bottom_Top_Cube.002_None_Top_Cube.002_None_bottom_Top
+s off
+f 6/1/1 5/2/1 2/3/1 1/4/1
+g Top_Cube.002_None_Top_Cube.002_None_bottom_Top_Cube.002_None_Top_Cube.002_None_bottom_Bottom
+f 11/5/2 10/6/2 14/7/2 13/8/2
+g Top_Cube.002_None_Top_Cube.002_None_bottom_Top_Cube.002_None_Top_Cube.002_None_bottom_Right-Left
+f 1/9/3 2/10/3 3/11/3 4/12/3
+f 5/13/4 6/1/4 7/14/4 8/15/4
+f 4/12/3 9/16/3 10/17/3 11/18/3
+f 12/19/4 7/14/4 13/8/4 14/20/4
+g Top_Cube.002_None_Top_Cube.002_None_bottom_Top_Cube.002_None_Top_Cube.002_None_bottom_Back
+f 6/21/5 1/9/5 4/12/5 7/22/5
+f 7/22/6 4/12/6 11/18/6 13/23/6
+g Top_Cube.002_None_Top_Cube.002_None_bottom_Top_Cube.002_None_Top_Cube.002_None_bottom_Front
+f 2/10/7 5/24/7 8/25/7 3/11/7
+f 9/16/8 12/26/8 14/27/8 10/17/8
+g Top_Cube.002_None_Top_Cube.002_None_bottom_Top_Cube.002_None_Top_Cube.002_None_bottom_Inside
+f 4/28/9 3/29/9 8/30/9 7/31/9
+f 7/31/10 12/32/10 9/33/10 4/28/10