Modification Wilson Cowan for reproducibility

Created by: lionelkusch

Hi all, I reopen a pull request on this topic. I am sorry, I didn't have the time to finish the last pull request : https://github.com/the-virtual-brain/tvb-library/pull/74 .

This pull request is to modification of the model Wilson Cowan for include the shift of the sigmoid present in the original model but not implemented. I included a jupyter-notebook for reproduce the figure 4 in Wilson Cowan and the figrue A1 in Daffertshofer and van Wijk (2011)