Distinguish color of orbit in solarmap for better direction indication

The solar map is orthogonally projected and doesn't use depth buffer,
which means the user have no clue whether the orbit ring is facing
toward or away from him.  Applying color difference to those cases
may help to interpret the direction.
Fix mouse highlight position of solar map window tip

Also refactored GLwindowSolarMap::drawSolarMap entirely.  Specifically,
added many comments.