Updated octopus map gen

[tadrinth]

Tweaked the Octopus map gen a bit.  It should have noticeably more variety now, but also have a better balance of planets between the center and the arms. In particular, it was always linking the center as a Gabriel graph; now it will occasionally use other methods. Also updated the comments. 

Mantis: https://bugtracker.arcengames.com/view.php?id=22553