WIP: "Statistics: Add more information"

Partially treats #81 (closed)

What does this MR do?

Adds counter for total food baskets and average baskets per week.

How confident are you it won't break things if deployed?

pretty sure. Might check that I used the database table correctly.

Links to related issues

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, merge request link, username(s))