Display ground track only for selected satellite

[danapple]

As an optional behavior, the multi-satellite view should display ground tracks only for the selected satellite. This would simplify switching ground tracks between satellites by alleviating the need to turn off ground track display for the previous satellite. In combination with issue #359 it would nicely keep the display highlighting information for the selected satellite.

[df7cb]

I would appreciate this feature. I just had to web search for how to display the ground track at all - there are context menus in too many places, and a bit of automation would help.