Many fixes and improvements for all of the R1rho dispersion models in the user manual.

The equations are now correct and the parameter table updated with new parameters and equations.
Removed the unused theta and R1 arguments for the lib.dispersion.m61.r1rho_M61() function.

These off-resonance parameters are not used in the on-resonance model.
Updated the r1rho_on_res_m61 dispersion on-resonance data for off-resonance models.

The chemical shifts are now the same for all spins, to force perfect on-resonance, and the two spins
are now different residues.