This commit switches to using the new 'typeData' interface for
representing type-specific aquifer data items. In particular we use
the new 'typeData.is<>()' and 'typeData.get<>()' member functions to
query and access the data that is specific to each aquifer type
(e.g., Carter-Tracy or numerical).
While here, also expand the reported data items for numerical
aquifers to one initial pressure value for each aquifer cell. This
is needed for restart purposes.
make it a template for grid types. this allows using
explicit template instantation and compile this code
only once per grid type, instead of once per simulator object.
