* fix(disqusjs): refactor local DisqusJS loading check for improved readability
* fix(gitalk): refactor local Gitalk loading check for improved readability
* add comment provider: DisqusJS
* Simplify `if` condition, and format code
* Load disqusjs.scss only when it's enabled
* Use `let` instead of `var`
Co-authored-by: sspirits <admin@lv5.moe>
Co-authored-by: Jimmy Cai <github@jimmycai.com>