Achievements: Show image usages, rather than images used #2705
Description
One of the goal of the Achievements activity is to show the user that their uploads are being useful.
Let's say a user has uploaded a very good picture of the Everest, and this picture is now used in the Wikipedias in English, Vietnamese, and 98 other languages.
Currently, the user would see Images Used: 1
Instead, we should show Images Usages: 100
Maybe it takes more time to compute.
Both client-side and server-side changes are needed.
The first task is to find the best web request for this.