Add lookup table for Hedgewars key IDs instead of generating IDs on the fly This makes sure the key IDs never change. Previous implementation abused SDL_GetScancodeName to generate the IDs programmatically, which was not reliable and explicitly adviced against in the SDL documentation <https://wiki.libsdl.org/SDL_GetScancodeName#Remarks>.

enable sdl_mixer opus support if possible

allow running plaintext and tls servers in parallel