Blocking buttons (#69)

![image](https://github.com/storytold/storyteller-bevy/assets/10954133/6c963b6c-6551-4379-854e-9f3f57cb173d)

---------

Co-authored-by: Danny McGee <dannymcgee@gmail.com>

studio-frontend/src/app/app.element.ts

@@ -31,6 +31,8 @@ import "@storyteller/studio-web/transform-toolbar";
 import "./anim-editor.element";
 import "./help.element";
 
+import "./blocking.element";
+
 import "./app.element.scss";
 
 @customElement("app-root")
@@ -149,6 +151,8 @@ export class AppElement extends LitElement {
 				<sts-anim-editor
 					class="timeline v-end h-start h-before-hierarchy"
 				></sts-anim-editor>
+
+				<sts-blocking></sts-blocking>
 			` : nothing}
 
 			<!-- Dialogs and modals -->