Add an option for a KCU to RamAirKite

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@ufechner7
I took a look at KitePodModels.jl, and it seems like the only thing it does is change the tether length directly. So I won't use the KCU, instead, I will make sure it is possible to change the segment length of the steering bridle lines between timesteps. Users could choose to use a KCU to set the segment lengths, but this would be outside SymbolicAWEModels.jl in an example.

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A KCU can be modeled as a point with extra mass and drag, like done for the V3 kite in the v3-kite branch. And then the segment lengths can be changed between steps.

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https://github.com/OpenSourceAWE/V3Kite.jl has a KCU