Created the Relax_disp.test_sprangers_data_to_mq_cr72 system test.
This was copied from the Relax_disp.test_sprangers_data_to_mq_ns_cpmg_2site system test and the
model changed to 'MQ CR72'.
This follows the tutorial for adding relaxation dispersion models at:
http://wiki.nmr-relax.com/Tutorial_for_adding_relaxation_dispersion_models_to_relax#The_test_suite
