- Linting (ESLint): Remove now unneeded config and add per new update

- Refactoring: Prefer for-of, event.key (newly enforced linting)
- Refactoring: Better var. names
- npm: Update devDeps and update local copies

editor/layer.js

@@ -141,8 +141,8 @@ class Layer {
    * @returns {void}
    */
   appendChildren (children) {
-    for (let i = 0; i < children.length; ++i) {
-      this.group_.append(children[i]);
+    for (const child of children) {
+      this.group_.append(child);
     }
   }