- l10n: Add Chinese (simplified) extension locales (Thanks, @enlove!)

- Linting (ESLint): Avoid reporting `no-console`
- Refactoring: Avoid Firefox console errors with hidden iframe
- Docs (CHANGES): Fix Markdown heading level

editor/extensions/ext-locale/helloworld/zh-CN.js

@@ -0,0 +1,9 @@
+export default {
+  name: 'Hello World',
+  text: 'Hello World!\n\n 请点击: {x}, {y}',
+  buttons: [
+    {
+      title: "输出 'Hello World'"
+    }
+  ]
+};