Allow different superposition models for wake and blockage + add blockage to flowmap with weightedSum (was missing before)

update WindTurbines.ipynb with GenericWindTurbine and GenericTIRhoWindTurbine examples + add 6% power loss in DTU10MW

fix #44

before default rotor center was shared among wind farm models, i.e. wakedeficit model of last instance was applied to all instances