Added object list to layers panel (#466)

Co-authored-by: Timo Dittmann <timo.dittmann@kaufland.com>

src/common/layer.js

@@ -146,6 +146,14 @@ class Layer {
     }
   }
 
+  /**
+  * Returns all children of this layer.
+  * @returns {NodeListOf<ChildNode>} The children of this layer.
+  */
+  getChildren () {
+    return this.group_.childNodes;
+  }
+
   /**
   * @returns {SVGTitleElement|null}
   */