GeodesicFEAssembler and RiemannianTRSolver now directly accept dune-functions bases

At least the harmonicmaps.cc example still works as before.
[caveat: only tested without HAVE_MPI]
Internally, at various places in the code, a dune-fufem basis is still constructed
from the dune-functions one.  These parts can be ported one by one, as dune-fufem
slowly replaces its own bases by the ones from dune-functions.

[[Imported from SVN: r10080]]