WindTurbineCluster takes only WindFarms but not WindTurbines

[uvchik]

The input of the WindTurbineCluster is a list of WindFarm objects. WindTurbine objects are not allowed. I think we should either rename the class or allow WindTurbine objects or both.

[uvchik]

What about WindFarmCluster?

[SabineHaas]

decision dev meeting:
Allow WindTurbines / WindTurbineGroups in WindTurbineCluster.