Earth updates, coordinate change for 3D, better trails (0.1.2/c)

Added nicer visuals to earth (kudos to @0xSabrina for advice, will add landmasses or clouds in the future), made trail look better with fading, and changed the coordinate axes (initially x-y because 2D, but then I wanted to change it to a top down view, and for a drop-in 3D implementation, now x-z (top down view for an equatorial orbit)

The earth now spins as well

Hopefully, next update works on the trajectory prediction, and then add the 3D camera
Long term, I’d like to add small lessons on orbital mechanics
As always, web demo updated, check it out :D