Consistent use of interface and internal types

[mnlevy1981]

I think we want some datatypes used by marbl_interface_class defined in marbl_interface_types.F90 and others defined in marbl_internal_types.F90 with the distinction being:

• Datatypes that are used by the GCM driver (explicitly via a use statement) should be in marbl_interface_types.F90, all others belong in marbl_internal_types.F90.

This will require some clean-up, as many of the datatypes in marbl_interface_types.F90 are not explicitly used by the driver (rather, the derived types appear as components of marbl_instance).

This will not affect the API at all, but it would be nice to be consistent before the 1.0.0 release.

[mnlevy1981]

Note that the file names have changed:

marbl_interface_types.F90 -> marbl_interface_public_types.F90
marbl_internal_types.F90 -> marbl_interface_private_types.F90

This ticket still stands, though: we need to come up with clear criteria for when to put derived types in each of these files (vs defining them in a separate module). I think this fits nicely in the "freeze development" column because it may result in some massive refactoring.

[mnlevy1981]

#311 and #314 should be kept in mind while addressing this ticket