Added the ZQ and DQ CPMG experiment types to the dispersion variables.
This is needed for the 'MQ NS CPMG 2-site' model change to 'MMQ 2-site' and follows from the post at
http://article.gmane.org/gmane.science.nmr.relax.devel/4734.
This follows the tutorial for adding relaxation dispersion models at:
http://wiki.nmr-relax.com/Tutorial_for_adding_relaxation_dispersion_models_to_relax#Creating_a_new_experiment_type.
