Problems on prediction_plot.py

[AlejandroGorgues]

While executing prediction_plot.py I found out two issues:

1. If I want to enable the deterministc option, I need the model attribute front_obj_thresholds. I found out that this key was initialized while executing plot_performance_diagrams.py on a old commit, and the current commit does not contains any option for that.
2. In the past I added the option for the calibration on this script, where the execution of the calibration script calibrate_model.py was needed. The problem is that in the statistics folder of the model, only exist spatial and temporal ncs, making not possible to calibrate as the script loads the full nc that the generate_performance_stats.py was creating in the past.

I solved the first one by adding the code from the older commit, however I cannot do it with the calibration.