Convert door model to B3D (#2906)

Using a B3D model I worked out that it would be possible to have only two models (instead of the current four) for the doors and still keep all the mirroring correct when the door is open/closed.

mods/doors/init.lua

@@ -448,16 +448,16 @@ function doors.register(name, def)
 	def.collision_box = {type = "fixed", fixed = {-1/2,-1/2,-1/2,1/2,3/2,-6/16}}
 	def.use_texture_alpha = "clip"
 
-	def.mesh = "door_a.obj"
+	def.mesh = "door_a.b3d"
 	minetest.register_node(":" .. name .. "_a", table.copy(def))
 
-	def.mesh = "door_b.obj"
+	def.mesh = "door_b.b3d"
 	minetest.register_node(":" .. name .. "_b", table.copy(def))
 
-	def.mesh = "door_a2.obj"
+	def.mesh = "door_b.b3d"
 	minetest.register_node(":" .. name .. "_c", table.copy(def))
 
-	def.mesh = "door_b2.obj"
+	def.mesh = "door_a.b3d"
 	minetest.register_node(":" .. name .. "_d", table.copy(def))
 
 	doors.registered_doors[name .. "_a"] = true

mods/doors/models/door_a.obj

@@ -1,40 +0,0 @@
-# Blender v2.76 (sub 0) OBJ File: 'door_a.blend'
-# www.blender.org
-mtllib door_a.mtl
-o door_a
-v 0.499000 -0.499000 -0.499000
-v 0.499000 1.499000 -0.499000
-v 0.499000 -0.499000 -0.375000
-v 0.499000 1.499000 -0.375000
-v -0.499000 -0.499000 -0.499000
-v -0.499000 1.499000 -0.499000
-v -0.499000 -0.499000 -0.375000
-v -0.499000 1.499000 -0.375000
-vt 0.842105 1.000000
-vt 0.894737 1.000000
-vt 0.894737 0.000000
-vt 0.842105 0.000000
-vt 0.421053 1.000000
-vt 0.421053 0.000000
-vt 0.947368 1.000000
-vt 0.947368 0.000000
-vt 0.000000 1.000000
-vt 0.000000 0.000000
-vt 1.000000 0.500000
-vt 0.947368 0.500000
-vt 1.000000 1.000000
-vt 1.000000 0.000000
-vn 1.000000 0.000000 0.000000
-vn 0.000000 0.000000 1.000000
-vn -1.000000 0.000000 0.000000
-vn 0.000000 0.000000 -1.000000
-vn 0.000000 -1.000000 0.000000
-vn 0.000000 1.000000 0.000000
-usemtl None
-s off
-f 2/1/1 4/2/1 3/3/1 1/4/1
-f 4/5/2 8/1/2 7/4/2 3/6/2
-f 8/2/3 6/7/3 5/8/3 7/3/3
-f 6/9/4 2/5/4 1/6/4 5/10/4
-f 1/11/5 3/12/5 7/7/5 5/13/5
-f 6/14/6 8/8/6 4/12/6 2/11/6

mods/doors/models/door_a2.obj

@@ -1,50 +0,0 @@
-# Blender v2.79 (sub 0) OBJ File: ''
-# www.blender.org
-mtllib door_a2.mtl
-o door_a2
-v -0.499000 1.499000 -0.499000
-v -0.499000 -0.499000 -0.499000
-v -0.499000 -0.499000 -0.375000
-v -0.499000 1.499000 -0.375000
-v 0.499000 -0.499000 -0.375000
-v 0.499000 1.499000 -0.375000
-v 0.499000 -0.499000 -0.499000
-v 0.499000 1.499000 -0.499000
-vt 0.894737 1.000000
-vt 0.894737 0.000000
-vt 0.842105 0.000000
-vt 0.842105 1.000000
-vt 0.421052 1.000000
-vt 0.421052 0.000000
-vt 0.000001 0.000000
-vt 0.000001 1.000000
-vt 0.894737 1.000000
-vt 0.894737 0.000000
-vt 0.947368 0.000000
-vt 0.947368 1.000000
-vt 0.842105 1.000000
-vt 0.842105 0.000000
-vt 0.421052 0.000000
-vt 0.421052 1.000000
-vt 0.947368 0.000000
-vt 0.947368 0.500000
-vt 1.000000 0.500000
-vt 1.000000 0.000000
-vt 1.000000 1.000000
-vt 1.000000 0.500000
-vt 0.947368 0.500000
-vt 0.947368 1.000000
-vn -1.0000 -0.0000 0.0000
-vn 0.0000 -0.0000 1.0000
-vn 1.0000 0.0000 0.0000
-vn 0.0000 0.0000 -1.0000
-vn 0.0000 -1.0000 0.0000
-vn 0.0000 1.0000 0.0000
-usemtl None.009
-s 1
-f 1/1/1 2/2/1 3/3/1 4/4/1
-f 4/5/2 3/6/2 5/7/2 6/8/2
-f 6/9/3 5/10/3 7/11/3 8/12/3
-f 8/13/4 7/14/4 2/15/4 1/16/4
-f 2/17/5 7/18/5 5/19/5 3/20/5
-f 8/21/6 1/22/6 4/23/6 6/24/6

mods/doors/models/door_b.obj

@@ -1,50 +0,0 @@
-# Blender v2.79 (sub 0) OBJ File: ''
-# www.blender.org
-mtllib door_b.mtl
-o door_b
-v 0.499000 1.499000 -0.499000
-v 0.499000 1.499000 -0.375000
-v 0.499000 -0.499000 -0.375000
-v 0.499000 -0.499000 -0.499000
-v -0.499000 1.499000 -0.375000
-v -0.499000 -0.499000 -0.375000
-v -0.499000 1.499000 -0.499000
-v -0.499000 -0.499000 -0.499000
-vt 0.894736 1.000000
-vt 0.947368 1.000000
-vt 0.947368 0.000000
-vt 0.894736 0.000000
-vt 0.842105 1.000000
-vt 0.421053 1.000000
-vt 0.421053 0.000000
-vt 0.842105 0.000000
-vt 0.842105 1.000000
-vt 0.894736 1.000000
-vt 0.894736 0.000000
-vt 0.842105 0.000000
-vt 0.421053 1.000000
-vt 0.000000 1.000000
-vt 0.000000 0.000000
-vt 0.421053 0.000000
-vt 1.000000 0.500000
-vt 0.947368 0.500000
-vt 0.947368 1.000000
-vt 1.000000 1.000000
-vt 1.000000 0.000000
-vt 0.947368 0.000000
-vt 0.947368 0.500000
-vt 1.000000 0.500000
-vn 1.0000 0.0000 0.0000
-vn 0.0000 -0.0000 1.0000
-vn -1.0000 0.0000 0.0000
-vn 0.0000 0.0000 -1.0000
-vn 0.0000 -1.0000 0.0000
-vn 0.0000 1.0000 0.0000
-usemtl None.007
-s 1
-f 1/1/1 2/2/1 3/3/1 4/4/1
-f 2/5/2 5/6/2 6/7/2 3/8/2
-f 5/9/3 7/10/3 8/11/3 6/12/3
-f 7/13/4 1/14/4 4/15/4 8/16/4
-f 4/17/5 3/18/5 6/19/5 8/20/5
-f 7/21/6 5/22/6 2/23/6 1/24/6

mods/doors/models/door_b2.obj

@@ -1,50 +0,0 @@
-# Blender v2.79 (sub 0) OBJ File: ''
-# www.blender.org
-mtllib door_b2.mtl
-o door_b2
-v 0.499000 1.499000 -0.499000
-v 0.499000 1.499000 -0.375000
-v 0.499000 -0.499000 -0.375000
-v 0.499000 -0.499000 -0.499000
-v -0.499000 1.499000 -0.375000
-v -0.499000 -0.499000 -0.375000
-v -0.499000 1.499000 -0.499000
-v -0.499000 -0.499000 -0.499000
-vt 0.842105 1.000000
-vt 0.894737 1.000000
-vt 0.894737 0.000000
-vt 0.842105 0.000000
-vt 0.421052 1.000000
-vt 0.000001 1.000000
-vt 0.000001 0.000000
-vt 0.421052 0.000000
-vt 0.894737 1.000000
-vt 0.947368 1.000000
-vt 0.947368 0.000000
-vt 0.894737 0.000000
-vt 0.842105 1.000000
-vt 0.421052 1.000000
-vt 0.421052 0.000000
-vt 0.842105 0.000000
-vt 1.000000 0.500000
-vt 0.947368 0.500000
-vt 0.947368 1.000000
-vt 1.000000 1.000000
-vt 1.000000 0.000000
-vt 0.947368 0.000000
-vt 0.947368 0.500000
-vt 1.000000 0.500000
-vn 1.0000 0.0000 0.0000
-vn 0.0000 -0.0000 1.0000
-vn -1.0000 0.0000 0.0000
-vn 0.0000 0.0000 -1.0000
-vn 0.0000 -1.0000 0.0000
-vn 0.0000 1.0000 0.0000
-usemtl None.010
-s 1
-f 1/1/1 2/2/1 3/3/1 4/4/1
-f 2/5/2 5/6/2 6/7/2 3/8/2
-f 5/9/3 7/10/3 8/11/3 6/12/3
-f 7/13/4 1/14/4 4/15/4 8/16/4
-f 4/17/5 3/18/5 6/19/5 8/20/5
-f 7/21/6 5/22/6 2/23/6 1/24/6