allows different benson_template_names
allows different benson_template_names

prior to this, I assumed that the names in the benson template would
also be {'varea', 'angle', 'eccen'}, but the most recent version of the
Benson template scripts use the names {'areas', 'angle', 'eccen'} (the
anatomical vs the fitted templates may also use different names), and so
to make this more robust, adds a dictionary benson_template_names to
_arrange_mgzs_into_dict that can handle this. the main function will
check whether varea or areas is correct (and raise an exception if it
can't find either). if there ends up being too much variation, I'll have
to come up with something else, but this works for a small number of
names

billbrod/spatial-frequency-preferences,billbrod/spatial-frequency-preferences,billbrod/spatial-frequency-preferences