Units in trajectory reference frames

[Carifio24]

This PR adds support for different units in trajectory reference frames. There are a few different parts to this PR:

• In the FrameWizardTrajectory window, the units dropdown currently doesn't actually trigger anything. This PR adds a listener that will change the TrajectoryUnits of the associated reference frame when the dropdown changes.
• TrajectorySample currently has a hard-coded factor of 1000 when returning its Position. This PR gives each TrajectorySample a unit type, and the appropriate factor is used when returning the position.
• When a trajectory reference frame has its units change, its trajectory is marked as 'dirty', so that the layer manager knows that the orbit needs to be redrawn.

[pkgw]

CC #91

[Carifio24]

I modified position to be a method that takes the altitude units as an input. This feels like a more natural way to ask for the position to me, and I don't expect there to be a significant difference between this and using the scale factor as the argument (the only time this gets called in a loop is when the orbit is refreshed after a unit change).

Note that there actually wasn't a serialization issue for this PR, since the trajectory positions X, Y, and Z were already stored in meters.