Work at Los Alamos (NM, USA) is supported by the US DOE Basic Sciences for the National Nuclear Security Administration of the US Department of Energy under Contract No. DE-AC52-06NA25396. Work on the project at Nordita (Stockholm, Sweden) is supported by the Swedish Research Council Grant No. 638-2013-9243, the Knut and Alice Wallenberg Foundation, and the European Research Council under the European Union’s Seventh Framework Program (FP/2207-2013)/ERC Grant Agreement No. DM-321031.