Added the 'NS 2-site 3D red' model to the relax_disp.select_model user function frontend.
This is the 'NS 2-site 3D' model with R20A = R20B = R20.
This commit follows step 2 of the relaxation dispersion model addition tutorial (http://thread.gmane.org/gmane.science.nmr.relax.devel/3907).
Authored by: bugman 2013-07-17
Parent: [r20348]
Child: [r20350]
