SaVi satellite constellation visualizer savi-dev

Supporting changing menus between different bodies,
so that we can offer different simulations for each
planet/moon. (The Clarke stationary script will see
reuse, but its comments would need tweaking, at least.)

Constellations menu is used in main/coverage/fisheye.
Locations menu is just used in fisheye.

Fixing menu typo: Med. Sean -> Sea

Updating note on simulating Mars/other bodies.

upating savi constants dialog to show new formatting, Earth/Mars popup.

Introducing planetary body C-side. Earth is 0, for now Mars is 1.

Also removing 'savi' command, which was duplicate of 'satellites', never used.

savi command as an alternative to satellites was never used. Shorter, though.

Reset to default now obeys planet setting.

there's a lot of cruft C-side around defaults.

Minor cleanup of display variables - they're an overlay params_display().

Improving Simulation constants.

We now call out the length of year, which, like tilt,
is used in pseudo-Sun calculations.

Equator and tropics do alternate pixels. so
if they're together (no tilt) it becomes a
solid line.