Add the checkbox quick button to the comment tool bar also (#12885)

Just copy it from the WIKI tool bar :)

Signed-off-by: a1012112796 <1012112796@qq.com>

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: zeripath <art27@cantab.net>

web_src/js/index.js

@@ -1484,7 +1484,26 @@ function setCommentSimpleMDE($editArea) {
     spellChecker: false,
     toolbar: ['bold', 'italic', 'strikethrough', '|',
       'heading-1', 'heading-2', 'heading-3', 'heading-bigger', 'heading-smaller', '|',
-      'code', 'quote', '|',
+      'code', 'quote', '|', {
+        name: 'checkbox-empty',
+        action(e) {
+          const cm = e.codemirror;
+          cm.replaceSelection(`\n- [ ] ${cm.getSelection()}`);
+          cm.focus();
+        },
+        className: 'fa fa-square-o',
+        title: 'Add Checkbox (empty)',
+      },
+      {
+        name: 'checkbox-checked',
+        action(e) {
+          const cm = e.codemirror;
+          cm.replaceSelection(`\n- [x] ${cm.getSelection()}`);
+          cm.focus();
+        },
+        className: 'fa fa-check-square-o',
+        title: 'Add Checkbox (checked)',
+      }, '|',
       'unordered-list', 'ordered-list', '|',
       'link', 'image', 'table', 'horizontal-rule', '|',
       'clean-block', '|',