Level class created and gravity editable.

tilorswift/js/menu/TilesetPickerWidget.js

@@ -42,6 +42,7 @@ export default class TilesetPickerWidget extends Widget
     {
         this.tileset = tileset;
         this.htmlElementSelector.innerHTML = '';
+        this.htmlElementSelector.style.width = Math.ceil(Math.sqrt(this.tileset.tiles))  * this.tileset.getTileWidth() + 'px';
         this.loadTileset();
     }