- adds missing header to files
- unify header
- add SPDX (https://spdx.dev/) identifier to header (first step for getting REUSE https://reuse.software/ compliant)
- reworked doxgen

- uses awesome doxygen theme: https://jothepro.github.io/doxygen-awesome-css/

Adresses: #183

- adds wiki pages to doxygen page
- adds doxygen modules for production code and tests

Merge branch 'develop_temp' of https://git.rz.tu-bs.de/h.alihussein/VirtualFluids_dev into develop_temp

Remove unused interface from Timer and exchanged UBTimer with new small Timer class which only uses chrono