Optimize visitor-facing JavaScript

Problem/Motivation

• Disqus JS (the one that comes from Disqus.com) is not the most optimal JS code and I don't think it's getting optimized any time soon. Thus, we should improve anything else that we can improve, e.g. disqus.js in the Disqus module.
• Not all sites use jQuery these days, mostly because core JS has a ton of new features.
• Disqus doesn't seem to use much jQuery, so ideally, the dependency on jQuery should be removed.

Proposed resolution

1. Allow lazy-loading ✨ Lazy load / async load Disqus libraries for better performance RTBC .
2. Once that issue is closed, the dependency on jQuery should be removed.
3. Possibly, the Disqus comment count and Disqus comment thread JS should be split into 2 files? Thus, sites will only load the code that will actually be used.

If a maintainer promises fast reviews and commits, I'd gladly volunteer to work on this issue to get things done fast :D In that case, feel free to assign the issue to me (Jigarius).