Level class created and gravity editable.

js/ImageLoader.js

@@ -0,0 +1,32 @@
+export default class ImageLoader
+{
+    images = [];
+    numberImagesLoaded = 0;
+
+    update()
+    {
+        this.numberImagesLoaded++;
+
+        if (this.numberImagesLoaded === this.images.length) {
+            window.dispatchEvent(new Event('imagesloaded'));
+        }
+    }
+
+    getCurrentProgress()
+    {
+        return this.numberImagesLoaded / this.images.length;
+    }
+
+    addImage(imagePath)
+    {
+        let image = new Image();
+        image.src = imagePath;
+        image.addEventListener(
+            'load', () => {
+                this.update();
+            }
+        );
+
+        this.images.push(image);
+    }
+}