significant re-write

Details:
- factorize the code in well-defined functions
- add docstrings explaining what I am doing
- rewrite most of this script. Now plotting and using the resulting
histograms as bins/counts that can be used for the unfolding.
- compute normalized response matrix
- add plotting functions
utils to write/read np.array from/to json
separate the generation from the unfolding

Details:
two separate logic steps: generate the pseudo-data, and then unfold.
The pseudo-data can come either from the json file, or be generated.
almost there, but pyfbu does not work

Details:
complaining about template. I thought it wasn't needed anymore.
Need to ask clement and Francesco about it.