Additional enhancements to the Discourse-based blog page

[notriddle]

After #219 is merged:

• [ ] Clicking on a link at the Janitor page should increment the visitor count within Discourse, giving us a measure of each link's popularity (that only needs to be additionally merged with the data from MailChimp). I think this just requires us to go through a URL like https://discourse.janitor.technology/clicks/track?url=URL&post_id=PID&topic_id=TID
• [ ] Show the frequent commenter's avatars next to the "N Comments" button, the same way the Discourse JavaScript version would do it
• [ ] The target="_blank" should be added by post-processing Discourse's cooked HTML, instead of by JavaScript. The link-click-counts should be added the same way
• [ ] The target="_blank" should be added to the "N Comments" butto
• [ ] Next to the headline, add a date, like the old one
• [ ] Use an API token, and potentially a rate limit, to synchronize
• [x] "1 comments" should be singular
• [ ] When visiting a blog post by #slug, put the post title below the header

[jankeromnes]

I'm not sure we want to enable link tracking on our blog page, it's useful in the newsletter, and fair enough that Discourse does it on its posts, but in our HTML page I'd prefer to have real links, even if we miss the information of how many people click on a link.