CGAL integration

The CGAL library is now a required dependency for PrusaSlicer. On Linux systems, one can use the provided dependency build scripts (under deps subdir) to obtain the library or use the system's package manager. The minimum version to use is 4.13.2. This version requirement is not stated in the CMake build scripts of PrusaSlicer. When building and installing CGAL from source as a header-only library, it exports the CMake config scripts needed by find_package and advertises an incompatibility between major version numbers. PrusaSlicer builds just fine with CGAL 4.x and 5.x versions. By stating a minimum version in find_package call, it would make the build fail for another (probably compatible) major version. Another issue is that when building CGAL 5.0 in header-only mode (CGAL_HEADER_ONLY), it will not install any CGALConfigVersion.cmake file. Subsequently, specifying any version requirement in the find_package() call will result in failure.