Progress on Maze Generation

* Implemented link creation based on link plans
* Improvised an implementation of door placement in DefaultDoorDecorator
for testing purposes. I'll provide a better version later.

Known issues:
1. Doors with one-way links to other rooms will generate a return door
at the destination. The return door doesn't actually lead back, it leads
to a new pocket. Need to disable pair generation for doors in mazes.
2. Consider weighing sections by the door capacity to avoid putting a
lot of doors into a small section. Also double-check that room selection
within sections is unbiased.

src/main/java/StevenDimDoors/mod_pocketDim/Point3D.java

@@ -62,6 +62,13 @@ public class Point3D implements Serializable {
 		this.y += y;
 		this.z += z;
 	}
+
+	public void add(Point3D other)
+	{
+		this.x += other.x;
+		this.y += other.y;
+		this.z += other.z;
+	}
 	
 	@Override
 	public Point3D clone()