Fixes for swapped indices in the relaxation evolution matrix for the 'NS R1rho 3-site' dispersion models.
Docstring fix for the lib.dispersion.ns_r1rho_3site module.
Added the Omega_A,B,C resonance offset parameter definitions to the dispersion chapter of the manual.
Updated the relax results for the synthetic data of the 'NS R1rho 3-site linear' dispersion model.
Modified the 'NS R1rho 2-site' dispersion model to match the 'NS R1rho 3-site' models.

The 6D evolution matrix indices have been rearranged to match the 9D matrix indices.  The tilt angle
for the initial magnetisation is no longer that for the average offset but that of state A, as was
changed for the 'NS R1rho 3-site' models earlier (r21911).  The system test was therefore updated
for the slightly different behaviour.