Last pull request before I leave

GA module now produces acceptable results and has some scripts to export them in excel files. Can now get time series of transfers within a cohort. Gen accounts and time series of IPL

TODO: create a new object level (name hypothsis_set ?) between simulation and cohort. This object shoudl regroup a set of attributes such as : 
- population
- profiles
- cohorts
- projection parameters
- aggregate_pv
- percapita_pv

Simulation will coordinate the different hypothesis_set and allow to do multiple comparison at once.
TODO: transform the scripts into true methods of simulation.