Fix for the synthetic data for the TP02 dispersion model.

The chemical shift is being set to that of state A, the major species, rather than the non-weighted
chemical shift average.  This could also have been set to the population weighted average.
The TP02 dispersion model now assumes the chemical shift is that of the major population A.

Previously the linear chemical shift average was assumed.
Increased the grid search size in the Relax_disp.test_r1rho_off_res_fixed_time_tp02 system test.

The previous two commits causes the optimisation to fail with the smaller grid size.