Compara species sets

Hi there,

The background colours that are used on the gene-tree display come from a list of species sets, that are stored in the Compara database
http://enssand-02.internal.sanger.ac.uk:9073/Homo_sapiens/Gene/Compara_Tree?g=ENSG00000139618;r=13:32889611-32973805

With e75, we'd like to move away from the old way we were storing the species sets (as an explicit list of genomes) to something with no maintenance (a reference to the taxon_id of the clade). The only difference in the webcode is in the ConfigPacker: it gets the species sets in a slightly different way.

The second commit simplifies the code a bit by making sure only the correct species sets are stored (it seems it might not have been always the case)

Cheers,
Matthieu