Implement missing methods for ram air kite

[ufechner7]

The following methods are not yet implemented, or not implemented correctly:

• find_steady_state!(s::RamAirKite)
• the property pos does not return an SVector of SVectors
• unstretched_length(s::RamAirKite)
• tether_length(s::RamAirKite)
• calc_height(s::RamAirKite)
• winch_force(s::RamAirKite)
• spring_forces(s::RamAirKite)

[1-Bart-1]

Do you need a property pos or can I implement a function pos(s::RamAirKite) instead?

[ufechner7]

A function pos() would be fine, but then it also needs to be implemented for KPS3 and KPS4 and the examples must be updated. And if I talk about examples, not only those in KiteModels but also those in KiteControllers and KiteSimulators.

[1-Bart-1]

So it would be easier to just add a property to the RamAirKite for now, and then we can move to just using SysState like in KiteViewers when we have time?