Add length control

[ufechner7]

add the parameters length and set_length to the function calc_acc, like this:

function calc_acceleration(wm::AbstractWinchModel, speed, force, length=nothing; set_torque=nothing, set_speed=nothing, set_length=nothing, use_brake = false)

This would be backwards compatible if length control is not needed.

If set_length is given and not nothing, then length must also be defined. The winch shall accelerate with max_acc (from settings.yaml) and with v_ro_max/ v_ro_min (from settings) until set_length is reached. If set_speed and set_length are provided, the norm of the speed shall be limited to set_speed.

[1-Bart-1]

As you said, this can be implemented using https://github.com/baggepinnen/TrajectoryLimiters.jl