This PR fixes all the remaining warnings in code when compiled with Qt6.
The code is still Qt5 and Qt6 compatible.
Most of the changes are boring, with the single exception of 6f5ad1f5d33aabfeff4e7cb266480e268ae9c84a that actually changes the way font weights are saved in the configuration files. Old values are migrated automatically.
This PR fixes all the remaining warnings in code when compiled with Qt6. The code is still Qt5 and Qt6 compatible. Most of the changes are boring, with the single exception of 6f5ad1f5d33aabfeff4e7cb266480e268ae9c84a that actually changes the way font weights are saved in the configuration files. Old values are migrated automatically.