This work was financed by Portuguese funds through Fundação para a Ciência e a Tecnologia (FCT), in the framework of project UID/BIM/04293/2013. M.M., J.C. and C.C. are also recipients of grants from FCT (SFRH/BD/80577/2011, SFRH/BPD/78187/2011 and SFRH/BPD/87071/2012, respectively).
- Received May 13, 2015.
- Accepted May 14, 2015.
- © 2015 The Author(s) Published by the Royal Society. All rights reserved.