Mcpdfs
Created by: Zaharid
This implements the filters discussed in:
https://indico.cern.ch/event/647565/contributions/2707845/attachments/1519217/2372593/kassabov.pdf
along with tools to visualize them. The interface could be better, in that it could use validphys.core.Filter and have a way to select the filters that get applied in the runcard (which probably can be done with a sufficiently clever production rule).
We also add a small class to plot the filtered replicas.
The x values are sampled differently which is why the number of outliers is different than in the slides. I am thinking on removing that filter altogether though.
While on it, rationalize a little bit how the writing of PDF sets works inside validphys. Now one decorator should take care of most things. I also removed some automated named functionality that I never liked too much and that I don't expect to be missed.
Closes #66 (closed).