Lazy-loading the main part of the app (#197)

* Splitting main part of app out of the main bundle.

Also improving the transition from intro to compressor.

* Showing error if app fails to load.

* lol these aren't async

* Please don't tell anyone I did this

* Spinner if user selects a file before the app has loaded. (#208)

src/components/Output/custom-els/PinchZoom/index.ts

@@ -272,10 +272,7 @@ export default class PinchZoom extends HTMLElement {
   private _stageElChange() {
     this._positioningEl = undefined;
 
-    if (this.children.length === 0) {
-      console.warn('There should be at least one child in <pinch-zoom>.');
-      return;
-    }
+    if (this.children.length === 0) return;
 
     this._positioningEl = this.children[0];