Resistive characteristic for current source based load
For some scenarios, we need a variable resistive load. The static RX load is not sufficient since every set point requires the calculation of a new system matrix. The CS based PQ load is a constant power load and does not behave as a resistance.
Therefore, a new load model has to be added that extends the CS based load with a resistive behaviour or it could be a new model composed of a current source and resistance.
This would solve the issue described in https://git.rwth-aachen.de/acs/public/simulation/cpowersystems/issues/40