Homogenize and compress NetCDF files

[skosukhin]

It would be nice to convert all NetCDF files in the repo to the same format and compress them.

Something like nccopy -4 -d 4 -s before.nc after.nc should do the job.

[RobertPincus]

Staged on develop in commit 122b662

Files in example/rfmip-clear-sky are left alone because they are traceable back to the ESGF

[skosukhin]

Currently, we have files in the classic and in the netCDF-4 formats. We can use the netCDF4 Python package to read both but it would be nice to be able to avoid the dependency on the NetCDF C library and use h5netcdf. Alas, it cannot read the classic format and we still need either netCDF4 or scipy, which is even heavier.

[RobertPincus]

@skosukhin Ah, so you want the files from ESGF to also be changed?

[skosukhin]

It was just a thought. If there are good arguments against changing the format for some files, I'm fine with not doing that.