Bring back ESMF_regrid

[huard]

Description

I think it was available in a previous version, and would be a starting point for discussions about the CSORR project's objectives.

[nilshempelmann]

There were regridding based on cdo commands. But switched it off while eliminating cdo due to dependency problems.
meanwhile functionallity moved to eggshell. if we find a solution for the dependencies in eggshell we can switch on cdo again.

https://github.com/bird-house/eggshell/blob/master/eggshell/nc/ocg_utils.py#L265