Updated the dispersion grid search function to user the loop_parameters() function.

This is an important fix as the specific_analyses.relax_disp.optimisation.grid_search_setup()
function was not matching the rest of the dispersion code, hence the parameters of the grid
increments and bounds were not matching the parameter vector, scaling matrix, target function
parameter depacking, etc.
Temporarily turned off the Relax_disp.test_sprangers_cpmg_data_auto_analysis system test.

This commit must be reverted!