Sky-Test-game

Adds a new game mode to Minetest - everything is floating islands!

For general information, visit the forum topic: https://forum.minetest.net/viewtopic.php?f=15&t=9255 For an excellent example on how best to enjoy this game, view Kilarin's exploration diary, Jacob's Ladder: https://forum.minetest.net/viewtopic.php?f=3&t=9695