tpl: Improve the built-in Disqus template (#3639)
tpl: Improve the built-in Disqus template (#3639)

* Improve the built-in Disqus template

  Set `disqus_identifier`, `disqus_title`, and `disqus_url`
  only if the user has explicitly provided them.

  Do not load Disqus when the website is previewed locally,
  otherwise it is very confusing.

* Use disqus_config instead of three global variables

  https://help.disqus.com/customer/portal/articles/472098-javascript-configuration-variables

anthonyfok/hugo,gohugoio/hugo,fedelibre/hugo,mdhender/hugo,fedelibre/hugo,anthonyfok/hugo,gohugoio/hugo,fedelibre/hugo,fedelibre/hugo,mdhender/hugo,anthonyfok/hugo,gohugoio/hugo,mdhender/hugo,mdhender/hugo