- 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/arrows/zh-CN.js

@@ -0,0 +1,19 @@
+export default {
+  name: '箭头',
+  langList: [
+    {id: 'arrow_none', textContent: '无箭头'}
+  ],
+  contextTools: [
+    {
+      title: '选择箭头类型',
+      options: {
+        none: '无箭头',
+        end: '---->',
+        start: '<----',
+        both: '<--->',
+        mid: '-->--',
+        mid_bk: '--<--'
+      }
+    }
+  ]
+};