Improve the installation procedure by using CMake install commands

This makes make install possible. The changes respect CMAKE_INSTALL_PREFIX, so if one adds -DCMAKE_INSTALL_PREFIX to the cmake .. command, it will install everything to there.

TODO: @Peyrer please fix the tests with the new and improved install paths. This should also fix issues with QuAPI not finding the preload path - in the most extreme case you could also add the new static CMake variable as a definition to the QuAPI library and use that directly.