ModelE, PISM and Restart Files

Set up a restart framework in GLINT2 that is compatible with ModelE, and works with PISM.

We shouldn't need to save much in GLINT2 (maybe just the reference date).  We do need some API support in GLINT2.  And we need to step PISM to the restart timepoint, and save in PISM.  The PISM restart file needs to be as-of the LAST PISM TIMESTEP (which may be up to 1 month before the restart file time).
