Allow for multiple budget years

[jdebacker]

I still don't understand OpenFisca-UK very well, but I think it can simulate policy for more than just one year.

If this is true, we should update get_micro_data.py to iterate over the years in the budget window (ideally, from start_year to the maximum year allowed by OpenFisca-UK.

[nikhilwoodruff]

Since this was filed, OpenFisca-UK can now simulate 2022-27 policy changes.