Implement savings plan with multiple durations

[caio-galvao]

The mathematical model was already adapted to support savings plans with multiple durations (e.g. 1 and 3 years at the same time). The implementation needs to be updated.

[fubica]

Didn't follow the comment. Given that the model already supports multiple durations, why the implementation needs to be updated?

[caio-galvao]

The implementation was written using an older version of the model.