Add an optional `[<count>]` UI to mark popularity

[throwaway34241]

Before you start.

• I have checked the Rejected Features page.
• I have searched the issue tracker for a feature request that matches the one I want to file, without success.

My great idea for Fraidycat is:

I would like to propose to add an OPTIONAL numerical value in the UI of each item, to denote some kind of popularity measure.

For example, when browsing Hacker News, a count can be added here, which would either denote the number of upvotes, or the number of comments.

What this popularity means for some other places:

• Medium: number of claps
• Twitter: number of likes or number of retweets
• Reddit: number of upvotes
• Youtube videos: number of likes or number of views
• Blog: number of comments (if possible to retrieve)

How to retrieve this popularity count can be defined inside social.json. It's of course optional, and omitting that field will just result in a empty UI (like the current one). It's therefore a non-breaking, purely additional change.

Further ideas:

• often, websites propose 2 popularity measures (like count + comment count), we could also add 2 numbers [<count1>, <count2>].