CHG: created external forcings for solid earth. Completely reorganized the sealevel change
core (in particular now we have a clean split between the external forcings, the grd core
and the dynamic steric core). Also, we reorganized and renamed the grd components and cores.
From eutatic, we now have: barystatic core, sal core, deformation core. No more diagnostics.
We also allow the external forcings to be mmes. Lots of cosmetic name changes (rise->change
for ex.).