Consolidate prokaryoticSectorDB

I merged all prokaryotic_MSA_sectorDatabase files into a single
loadable variable. Please, use prokaryoticSecorDB.mat from now on ! It
should only contain sectors with identified sequence. Because some MSA
linked to protein complex pdb files.
aaSectorDBCount function

For PCA on residue: count the occurrence of each aa in each sector in
the sectorDB given in argument.
Bug fixes on helper function