Replace custom comment hardcoded HTML with include

Also add custom_scripts.html include for custom comment provider JavaScript that loads in the footer.

Close #2549

fix: Do not redirect user away from site after they submit a comment (#2402)

Adjust comments to be compatible with compress_html (#2373)

Remove Google+

Google+ is being shutdown on April 2, 2019. Social sharing buttong, comment provider, and author link configs have been removed from the theme.

ref: https://support.google.com/plus/answer/9195133

Add support to customize `issue-term` (#2022)

Current we hardcoded the `pathname` for `issue-term` when we are using utterances comment provider.

It would be better for let users customize it by setting a `site.comments.utterances.issue_term` in their `_config.yml`.

Remove unused variables (#1996)

Add support for utterances (#1966)

* Add support for utterances
* Add utterances config documentation
* Update CHANGELOG and history

Close #1909 

Upgrade Font Awesome to version 5 (#1446)

Upgrade Font Awesome to version 5 (SVG with JavaScript)

Close #1396

Add Staticman v2 form scripts

Add support for Staticman v2 endpoint and reCAPTCHA

Ref: #803

Remove `#disqus_thread` duplicate

`<section id="disqus_thread"></section>` is set in `_includes/comments.html` and not needed in `_includes/comment-provider/disqus.html`.

Fixes #1199

Replace old Disqus script with Universal Embed Code (#1179)

* update embeddable disqus javascript

* Update disqus.html

Merge branch 'zmsp-master'

Fix indentation and remove comments

Google+ page comments updated.

Merge branch 'release/4.1.0'

Fix link to Discourse.org homepage in noscript section (#699)

Merge branch 'release/4.0.5' into develop

Replace `base_path` with `absolute_url` filter

Merge branch 'hotfix/3.4.2' into develop