Feature request: use of non gauged stations in the network

The idea is to be able to integrate GR models in the network with parameters dependant of neighbour sub-basins.

Ungauged stations

Todo:

• Add SubGraph containing ungauged stations in plot.GRiwrm
• Adapt CreateInputsModel.GRiwrm for handling ungauged nodes
• Create a function that creates a RunModel function including the modelling of ungauged nodes for run in Calibration
• Modify Calibration.GRiwrmInputsModel for calibrate the model above and set the calibration parameters for each sub-basin