Link all libraries to targets in add_dune_all_flags

The libraries are taken from DUNE_LIBS and from the
global property ALL_PKG_LIBS. This change is necessary
to drop the add_dune_*_flags macros in the future.
[CMake] Adjust find scripts to update the ALL_PKG_LIBS property
[CMake] Also append the LAPACK libs to ALL_PKG_LIBS

We dont provide a custom find module, so we need to update
the property after executing the system wide find module.