compute_ipl method fixed

One has to submit only cohorts with aggregated values in order to computes the IPL.
Added plots in Carole_Bonnet2.py
Expanded pyplot part of C_Bonnet2.py

Imported data from Carole Bonnet to compare with our results
The .xls file containing Carole's data
Merge pull request #22 from jsantoul/master

Expanded pyplot part of C_Bonnet2.py