#PickhardtPayments: fast mode: only add first one or two arcs per edge

[C-Otto]

Is your feature request related to a problem? Please describe.
The current implementation splits each channel into a few (by default: 5) parts in order to linearize the cost function. The first few parts are "cheaper" and, as such, it is less likely that the following parts will contribute to an MPP.

Describe the solution you'd like
Add an optional "fast mode" where for each channel only the first one or two parts are added (as arcs).