New activity: guess24

[Johnny Jazeix]

Hi,

Bruno (who also developed the grammar activities [1]) developed a new
activity in the master branch: guess24. The aim is to find 24 from 4
numbers and the provided operations (among +, -, *, /).

Feel free to test it and raise if there is any issue or possible improvement.

Thank you Bruno for this addition (and Timothée for the graphics update)!

Cheers,

Johnny

[1]: https://mail.kde.org/pipermail/gcompris-devel/2023-July/006273.html