day-night loop, dynamic skybox, clock on debug panel

res/shaders/background.glslf

@@ -0,0 +1,11 @@
+#version 330 core
+
+in vec3 v_coord;
+out vec4 f_color;
+
+uniform samplerCube u_cubemap;
+
+void main(){
+	vec3 dir = normalize(v_coord);
+	f_color = texture(u_cubemap, dir);
+}