Add wall shadow shaders

shader/wallShadow.vert

@@ -0,0 +1,11 @@
+#version 430 core
+layout (location = 0) in vec4 poss;
+layout (location = 1) in vec4 backPoss;
+
+out vec4 vBackPoss;
+
+void main()
+{
+  gl_Position = poss;
+  vBackPoss = backPoss;
+}