Add skybox rendering support

resources/shaders/skybox.vert

@@ -0,0 +1,15 @@
+#version 330 core
+
+in vec3 position;
+
+uniform mat4 view;
+
+uniform mat4 projection;
+
+out vec3 direction;
+
+void main() {
+    direction = position;
+    vec4 pos = projection * view * vec4(position, 1.0);
+    gl_Position = pos.xyww;
+}