Add ERA Interim fields

Start collecting ERA-Interim data by downloading the following:

• https://cera-www.dkrz.de/WDCC/ui/Entry.jsp?acronym=ERAIN_SFC12_MM_EWSS_180
• https://cera-www.dkrz.de/WDCC/ui/Entry.jsp?acronym=ERAIN_SFC12_MM_NSSS_181

We need Jblob and something like the following I used to get similar ERA40 fields:

for ds in ERA40_SFC06_MM_EWSS ERA40_SFC06_MM_NSSS ; do

    # download using JBlob
    java -cp software/Jblob-2.0.10/Jblob.jar:software/Jblob-2.0.10/commons-codec-1.4.jar \
        de.dkrz.cera.applications.JblobClient \
        --username willi_rath --password XXXXXXXXXX \
        --dataset $ds 

    # convert using CDO
    cdo -t ecmwf -f nc -copy -remapcon,r720x360 -setgridtype,regular ${ds}_1-540.grb ${ds}_1-540.nc
done

Ideally, we'd be able to just maintain a list of data-set names (ERAIN_SFC12_MM_EWSS_180, ERAIN_SFC12_MM_NSSS_181) and have a script that gets all data.

(cc: @joke-luebbecke)