[No Bug] Use CMake for PokerTH build

[tobbi]

I tried time and time again to build PokerTH using qmake and I was hit with build errors, outdated, hardcoded dependencies in the `third_party` directory and other things.

I think it would be much easier to write the makefile using CMake. It allows us to dynamically generate a makefile that doesn't need to be adapted to the target system, thus making builds much easier.

I can't promise much, but I *might* give it a try in the upcoming weeks.

[tobbi]

I was able to get a working (hacky) build:
https://github.com/tobbi/pokerth/tree/cmake-build

[tobbi]

I've submitted a few pull requests on the main repo.

I don't know if anyone can review them, but I'd appreciate it.