add serializable to polygon intersection

CityDoctorParent/CityDoctorModel/src/main/java/de/hft/stuttgart/citydoctor2/utils/PolygonIntersection.java

@@ -18,6 +18,7 @@
  */
 package de.hft.stuttgart.citydoctor2.utils;
 
+import java.io.Serializable;
 import java.util.List;
 
 import de.hft.stuttgart.citydoctor2.datastructure.ConcretePolygon;
@@ -30,7 +31,9 @@ import de.hft.stuttgart.citydoctor2.math.Segment3d;
  * @author Matthias Betz
  *
  */
-public class PolygonIntersection {
+public class PolygonIntersection implements Serializable {
+
+	private static final long serialVersionUID = -6301963226688351725L;
 
 	public enum IntersectionType {
 		NONE, LINE, POLYGON