Allow Skybox to take a Color (#57)

This PR Adds the ability to set the color of the skybox using the URL
parameters.

- Now you can pass a color's hexadecimal number (without the #) in the
  skybox parameter, and that will set the skybox to that color.

studio/src/wasm/init.rs

@@ -6,19 +6,10 @@ use crate::{InitAsset, InitParams, StudioMode, ViewportSize};
 
 #[wasm_bindgen(typescript_custom_section)]
 const WASM_ENTRY_POINTS: &str = r#"
-export type SkyboxId
-    = "gum_trees_4k"
-    | "kloofenfal_28d_misty_4k"
-    | "meadow_4k"
-    | "promenade_de_vidy_4k"
-    | "scythian_tombs_4k"
-    | "test_scene"
-    ;
-
 export interface InitOptions {
     mode: StudioMode;
     /** Required for all entry-points except `initFromStorytellerScene()` */
-    skyboxId?: SkyboxId;
+    skyboxId?: string;
     canvasSelector: string;
     canvasAlt: string;
     viewportSize: ViewportSize;