Rover: Obstacle Placement on Crater Terrain is Inconsistent

[MichaelFriebel]

The vertical placement of obstacles on crater terrain is often inconsistent, with some obstacles placed too low and others too high relative to the terrain's height. This is due to a temporary hack in new.obstacle() pending the changes needed in util.findTerrainHeight() and util.findTerrainSlope() to properly handle crater terrain polygons.