The Spanish Ministry of Economy and Competitiveness, through the Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2011-0075) and FEDER grant ECO2008-04756 (Grupo Consolidado-C), and from the Generalitat de Catalunya, through the prize “ICREA Acadèmia”for excellence in research and grants SGR2009-419 and SGR2014-515