Implement a single length penalty in the capacity function

[danoan]

Currently, the length component is only computed at the validation step. No length component is considered in the computation of the minimum cut.

This improvement aims to implement a very simple length penalization component in the capacity function, by simply adding a constant (weigthed by the length penalization parameter alpha) in the capacity function of each edge.

Ideally, we should use a convergent estimator, such as the one proposed by Boykov.