Add a counter for the amount of EN / NL sites #4

It would be nice for teachers to have an idea of how many Dutch and English websites have been added.

I imagine the top of the /beheer index page is a nice place to put it.

Something like this is what I'm thinking of:

Source: https://freefrontend.com/bootstrap-counters/

That source uses bootstrap, but I don't want to use bootstrap. Instead we should implement it with TailwindCSS