This seems necessary, so maybe we should not support single field analysis of relaxation dispersion
at all.
-> Kovrigin et al. (2006) JMagRes, 180: 93-104.
...
The changes made here are only a first draft and may not work. In particular, maybe the
spectrum.read_intensities(), relax_disp.cpmg_frq(), spectrum.replicated(),
spectrum.error_analysis(), and deselect.read() functions will need to know the magnetic field to
which the particular dataset is associated...
In fact, the different datasets should be input first and their R2eff calculated indepentantly. In
a second step, the actual relaxation dispersion curve fitting should be made with all data.
