V10lator

CI: Change Linux build to Docker container

1

This changes the build system to docker, unifying CI and user build environments. It disables caching atm but might be possible to re-add it with something like https://github.com/marketplace/actions/docker-cache

### Bug description Tried to delete large games. Lurtis said it moved them to Trash but KDE Trash still empty. Space still occupied. Game folder empty. So where did Lutris...

Math cleanup and optional new PRNG

4

THis removes some duplicated math function, removes local return values from math functions and adds the option to use the pseudo random number generator of the C library.