Scene storage backend integration (#51)

This PR adds Storyteller.ai API integration for saving and loading
Storyteller Studio scenes to/from the backend.

### Known issues
* The skybox is not currently stored in the serialized scene format

studio-web/src/lib/editor.element.ts

@@ -0,0 +1,28 @@
+import * as studio from "@storyteller/studio";
+import { ViewportSize } from "@storyteller/studio";
+import { PropertyValues } from "lit";
+import { customElement, property } from "lit/decorators.js";
+
+import { StudioBaseElement } from "./studio-base.element";
+
+@customElement("sts-editor")
+export class EditorElement extends StudioBaseElement {
+	@property() scenePath?: string;
+
+	onStart(viewportSize: ViewportSize): void {
+		if (!this.scenePath) return;
+
+		studio.startEditor(
+			this.scenePath,
+			`#${this._canvasProvider!.canvasId}`,
+			"Storyteller Studio",
+			viewportSize,
+		);
+	}
+
+	onChanges(changes: PropertyValues<this>): void {
+		if (changes.has("scenePath") && !!this.scenePath) {
+			// TODO
+		}
+	}
+}