Support normalizing values in KeyValueTree

Support normalizing values in KeyValueTree

Make it possible to normalize values stored in a KeyValueTree to match
an Options structure.  This makes the types etc. consistent in the tree.
This is mainly useful for reducing variability in tpr files for better
forward/backward compatibility management, but can also be nice for
producing consistent mdp output files from grompp (if we want to keep
that feature).

Change-Id: Ib5ea03faaa690c84076c1ada0c0a08ddf9a1a128