[server] Make *Reference classes implement ICloneable

Nibriboard/RippleSpace/ChunkReference.cs

@@ -90,5 +90,14 @@ namespace Nibriboard.RippleSpace
 				y
 			);
 		}
+
+		/// <summary>
+		/// Returns a clone of this ChunkReference.
+		/// </summary>
+		/// <returns>The newly-cloned instance.</returns>
+		public override object Clone()
+		{
+			return new ChunkReference(Plane, X, Y);
+		}
 	}
 }

Nibriboard/RippleSpace/LocationReference.cs

@@ -67,5 +67,14 @@ namespace Nibriboard.RippleSpace
 				y
 			);
 		}
+
+		/// <summary>
+		/// Returns a clone of this LocationReference.
+		/// </summary>
+		/// <returns>The newly-cloned instance.</returns>
+		public override object Clone()
+		{
+			return new LocationReference(Plane, X, Y);
+		}
 	}
 }

Nibriboard/RippleSpace/Reference.cs

@@ -5,7 +5,7 @@ namespace Nibriboard.RippleSpace
 	/// <summary>
 	/// An abstract class representing a coordinate reference to a location.
 	/// </summary>
-	public abstract class Reference
+	public abstract class Reference : ICloneable
 	{
 		public readonly Plane Plane;
 
@@ -22,5 +22,7 @@ namespace Nibriboard.RippleSpace
 		{
 			return $"({X}, {Y}, {Plane.Name})";
 		}
+
+		public abstract object Clone();
 	}
 }