libdunepdelab does not link as a shared library with dune_enable_all_packages()

When trying to build PDELab with the new dune_enable_all_packages() support and shared libraries, I get a linker failure in libdunepdelab because the linker cannot find some MPI symbols. The problem here is that we did not explicitly add all package flags to the library target.

I'll try and get some upstream support in dune-common to make this process a little easier (specifically a dune_target_enable_all_packages() macro).