The work of YV was supported by the following grants: Fonds de la Recherche Scientifique Médicale (FRSM) 3.4.525.08.F in 2008, 2010 & 2012, Fonds Spécial de Recherche (FSR) grant from the Université Catholique de Louvain (UCL) in 2008 & 2010, and Fondation Van Goethem-Brichant; The work of SL was supported by UCL FSR grants in 2008 and 2010, and by a grant from the Fondation Mont-Godinne 2012.