Several changes:

Changed XYZ stuff in SkyPoint and SkyMap to use Quaternions; added quaternion.[h|cpp] as part of this. We still aren't actually using this code, but it's in place for when we are ready to try it.

Removed SatelliteTrack class; moved its functionality to SatelliteComponent. Added SatelliteComposite to manage the SatelliteComponents. The code is ready to start testing actual satellite tracks in the sky map.

MilkyWayComponent is now derived from LineListComponent. I tried to make this class work properly with the new SkyMap::toScreen(SkyLine) function, but it got too complicated. The problem is that this function truncates lines at the edge of the screen, which messes up the construction of the MW polygons. Rather that try to deal with all the corner cases, I simply added a bool option to SkyMap::toScreen(SkyLine) that allows you to deactivate the truncation of lines at the screen edge. So Milky Way polygons will exist beyond the borders of the SkyMap.