Modernize Doxygen CSS

[cor3ntin]

I was made aware of the existence of Doxygen Awesome, that is a better-looking/more-modern theme for Doxygen.

It is deployed on large projects just as OpenCV https://docs.opencv.org/5.x/dc/d84/group__core__basic.html and it looks more readable than LLVM's documentation
https://clang.llvm.org/doxygen/classclang_1_1Sema.html

Given the installation only seem to require installing a few files, and the license is MIT, it might be worth investigating whether we use it for our Doxygen documentation.

[KaruroChori]

https://jigsaw.w3.org/css-validator/validator?uri=https%3A%2F%2Fdocs.opencv.org%2F5.x%2Fd4%2Fd17%2Fnamespacecv_1_1aruco.html&profile=css3svg&usermedium=all&warning=1&vextwarning=&lang=en

https://jigsaw.w3.org/css-validator/validator?uri=https%3A%2F%2Fdocs.opencv.org%2F4.10.0%2Fd4%2Fd17%2Fnamespacecv_1_1aruco.html&profile=css3svg&usermedium=all&warning=1&vextwarning=&lang=en

The comparison is between the new and old page of opencv docs.

I think it would be nice to address the CSS issues introduced upstream. They are all minor, but it would be bad considering the perfect score it could have.

(for reference jothepro/doxygen-awesome-css#182)