This fixes name clashes with DUNE's own factory that is introduced
in DUNE 2.7. Hence it closes issue #2266.
BTW: Dune's factory has more template parameters than ours.
This replaces the makePreconditoner() function. The main advantage
is that it is extensible, making it easy to for example add new
preconditioners to the factory at runtime. It supports both parallel
and serial preconditioners.