Move third party stuff out of src tree.

This gigantic commit (sry for that) moves all 3rd party stuff into
thirdpary. I also checks if these libraries are available on the
system (i. e. if cmake can find them) and builds them otherwise.

I got rid of the msvc build files.

PSP builds, qt console builds, qt widget builds and sdl 2 builds
work fine on linux that way. The next step is to fix everything
that I have broken on the other target platforms.