Changed the Noe auto-analysis to properly handle the peak intensity Grace plots.
This relates to bug #21863 (https://gna.org/bugs/?21863), the grace.write user function not being
able to write ref/sat plots as described in sample script noe.py.
Instead of trying to produce the 'ref.agr' and 'sat.agr' files for the non-existent 'ref' and 'sat'
parameters, instead the 'intensities.agr' file is being produced for the peak intensity parameter.
The reference and saturated intensities will appear as two graph sets within that plot.
