The function retrieves the Jump nodes (JNs) from a GO-level. JNs are those GO-terms which have
at least one child term not present in the level below it. If the optional parameter "organism" is
missing then the results are from the general GO tree. The supported organisms are "Homo sapiens / Human",
"Rattus norvegicus / Rat", "Mus musculus / Mouse", "Danio rerio / Zebrafish",
"Caenorhabditis elegans / Worm" ,"Arabidopsis thaliana / Cress", "Saccharomyces cerevisiae / Yeast",
"Schizosaccharomyces pombe / Fission yeast",
"Drosophila melanogaster / Fruit fly", "Escherichia coli / E.coli".