This commit removes all qmake-related build-files from the system. We
have now migrated to cmake and are no longer maintaining qmake anyways
and therefore there is no reason to keep it.
Removing it also clearly states to any potential user/programmer that
this project is no longer intended to be compiled with qmake.
Given that the .pri files no longer exist, the mumble-version.py script
had to be adapted to read the version from the CMakeLists.txt file
instead.
Furthermore a few of the submodules support cmake natively and therefore
we no longer need the src/buid-directory approach in order to build
them. The respective build dirs have been removed and the src-dirs have
been renamed.
