Fixes for the relax_disp.plot_disp_curves user function - the colours behaviour is now back to normal.

This does not affect relax 3.1.0 and is only a recent bug.
Updated two dispersion scripts in the test data directories to work with the current design.
Updated more test suite scripts to call the relax_disp.cpmg_frq user function.
The 'CR72' and 'MMQ CR72' models are now classified as nested in the dispersion auto-analysis.

The grid search for the 'MMQ CR72' model will therefore be skipped and the parameters taken from the
'CR72' model.  This will however rarely, if ever, be used.