Add a setting for power split that allow to direct power flow up until a given value

[florentLutz]

As of now, the dc splitter direct power flow in the two input based on a ration between power at one input and powre at the output. It could be interesting to allow user to chose an altenative mode were the amount of power directed in the primary input corresponds to either a fixed value or to anything below that value.

[florentLutz]

An option would do the trick

[florentLutz]

Done in #19 Is indeed an option