Fix a terrible bug with rotated orbits

So, how this basically worked was that we calculated where the
planet would be in orbit at time T around its center (the star)
X, Y by calculating Px, Py where the planet is at T, and then
translated by the amount of skew around the star that it's
orbit takes.

Now, there's one obvious bug there, in that the rotation takes
place after the point is found, so the center of rotation has
also been moved. Taking that into account, now all of the generated
planets will orbit around their stars again.

Also: color planets somewhat differently. I'd like this to be based
on some attributes of the planets themselves, but I'm happy with this
for now.
Center the frame for the window on screen

Initially the frame was only 800x600 but then I bumped it to
1280x800 and then 1480x800 when I added a sidebar. The last
change wrecked how the window's origin point was directly
in the center of the screen, so the window would be centered,
so this change should fix that.