Package download counter

[samuel-emrys]

It would be really useful to understand how much demand there is for different packages with a download counter. This helps organisations justify time spent supporting libraries and even helps us convince them to modify their behaviours to better support packaging practices. It would be good to have the following for each package:

• Lifetime (all package versions/revisions) download counter
• Version download counter

This has been opened to replace #71, which was closed as complete when this feature was originally added. Since its removal because there were some unforeseen complexities, this ticket has been opened to track that this is still an open request.