Think of better API to set plotting frame for 2D figures

Currently, we can set frame by passing *Orbit.pqw() in set_frame which is not user friendly and not intuitive.

---

Current status as of the last edit:

• We still don’t have a fine control over the plane, there are only two options available. Do we want/need to add more?
  • Or should I say three? At this point I’m not even sure Planes.BODY_FIXED should be a “plane”.
• Even if we can set the plane, we can’t set the reference direction directly: only using .set_orbit_frame or .set_body_frame (which at the moment calls *orbit.pqw(), but that’s an implementation detail). Do we want a method to change this?

[astrojuanlu]

This was addressed in #891:

This adds a new method to all orbit plotters, plot_body_orbit, that “Plots complete revolution of body and current position if given”, and another two for 2D orbit plotters, set_orbit_frame and set_body_frame. The former avoids calling Orbit.from_body_ephem (about to be removed), and the latter avoid the need to call set_frame(*orbit.pqw()), which is ugly, impossible to understand, and in general shouldn’t be there.

Now all the details about how the frame is set are hidden inside these functions, which frees us from refactoring them internally while maintaining this new API, which I think is acceptable. OrbitPlotter2D.set_frame and its static counterpart are deprecated now.

On the other hand, our original objective, which was producing plots in the Geocentric Solar Ecliptic frame that you added in #562, is a little bit closer, because the fundamental plane of GSE happens to be the same as Planes.EARTH_ECLIPTIC. However:

• We still don’t have a fine control over the plane, there are only two options available. Do we want/need to add more?
  • Or should I say three? At this point I’m not even sure Planes.BODY_FIXED should be a “plane”.
• Even if we can set the plane, we can’t set the reference direction directly: only using .set_orbit_frame or .set_body_frame (which at the moment calls *orbit.pqw(), but that’s an implementation detail). Do we want a method to change this?

I am changing the title (and scope) of this issue to reflect the current status.

[astrojuanlu]

We should remove this pqw stuff, it’s just a hack. Too inconsistent and fragile to be generally useful.