Fix too large file sizes of the final netcdf files

[SimonTreu]

Maybe that is already better after #95 is fixed. If not the compression in attrici.postprocess.py rechunk_netcdf needs to be changed by varying the deflation level in

"ncks -4 -O --deflate 5 --cnk_plc=g3d --cnk_dmn=lat,360 --cnk_dmn=lon,720 " 
+ str(ncfile) 
+ " " 
+ ncfile_rechunked