- Refactoring: Avoid unnecessary addEventListener false; change internal

jPicker function to class (used with `new`)
- Linting (ESLint): Add `valid-jsdoc` rule and make fixes; but turn off for
  now due to <https://github.com/eslint/eslint/issues/11036> and
  <https://github.com/eslint/eslint/issues/11037>
- Docs (JSDoc): Add some Markdown for variables, line breaks; tighten checks
  for overly generic types (though allow for `.Function` as in
  `jQuery.Function`) and avoid one previously missed instance

editor/extensions/ext-storage.js

@@ -101,6 +101,7 @@ export default {
     *       content into storage)
     * 2. Use localStorage to set SVG contents (potentially too large to allow in cookies)
     * 3. Use localStorage (where available) or cookies to set preferences.
+    * @returns {undefined}
     */
     function setupBeforeUnloadListener () {
       window.addEventListener('beforeunload', function (e) {
@@ -135,7 +136,7 @@ export default {
             }
           }
         }
-      }, false);
+      });
     }
 
     let loaded = false;