COrE (Cosmic Origins Explorer) A White Paper by Collaboration, TC, Armitage-Caplan, C, Avillez, M, Barbosa, D, Banday, A, Bartolo, N, Battye, R, Bernard, J, Bernardis, P, Basak, S, Bersanelli, M, Bielewicz, P, Bonaldi, A, Bucher, M, Bouchet, F, Boulanger, F, Burigana, C, Camus, P, Challinor, A, Chongchitnan, S, Clements, D, Colafrancesco, S, Delabrouille, J, Petris, MD, Zotti, G