Admin: calculate stats from admin page

[functionzz]

This PR allows admins to calculate all project statistics directly via the /admin page, which removes the need for using the ./manage.py calculate_stats command via the python shell.

Fixes #3879.

[functionzz]

I would also like to rewrite the current admin.js as it seems to not be written in jQuery.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 57.89474% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.07%. Comparing base (d3823b8) to head (90f962e).
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[mathjazz]

Great work!

We should probably just calculate stats of the enabled projects, right @flodolo?

Also, I'd move the button (perhaps called "Re-calculate stats"?) outside the search / filter area to the top right corner of the header of the page (see the position of the dropdwn on the Team pages).

[flodolo]

We should probably just calculate stats of the enabled projects, right @flodolo?

Yes, no point in running it on obsolete projects.

[flodolo]

We probably want to mention this in documentation, and why/when it might be needed?

[flodolo]

We probably want to mention this in documentation, and why/when it might be needed?

Would it make sense to put it in Maintenance?

[mathjazz]

Nice job!