New Earth Satellite tracks!

The display shows a curve across the sky, which is the path of a satellite over the next hour from the current location. The color of the curve can be modified, and you can toggle whether satellite tracks are drawn in the Solar System tab of the Options window.

TODO:
+ Right now, only three satellites are included: HST, ISS, and UARS. Many more are available, these are just for testing the feature.

+ Need to add satellite data to the Get New Stuff mechanism

+ Add tickmarks to the tracks, indicating the time of the passage

+ The path should be darkened where the satellite is in Earth's shadow (this information is already available, it's just a matter of using it).

+ Make thickness of the line proportional to brightness of the satellite?