Add Fediverse Infrastructure for app comments, ratings, download statistics for login in client app

Comment, rating and statistics issue has been discussed many times before (see #53 (closed) #646 (closed)). But I wanted to bring a new perspective with the Fediverse/ActivityPub infrastructure that can solve potential problems that are not considered in these discussions.

PLEASE read this first: repomaker#268 (closed) (for fediverse logic and backend implementation)

In F-droid Client:

• We should see download statistics, ratings and comments for each app -that upstream repository support download count-
• We should be able to login with connecting an external fediverse account1 AND/OR creating a new f-droid fediverse account2
• We should be able to create new comment with our fediverse identity (asandikci@mastodon.social -for 1- or asandikci@f-droid.org -for 2- for example)
• We should be able to rate app(x/5) OR like app -should be discussed-
• We should be able to sort apps for their rating or download count ...

Please indicate your opinions and positive/negative aspects in the comments. I'm sorry if it's complicated, feel free to ask questions (and I'm not a native English speaker, sorry for the spelling mistakes)