add helper to build new vehicle based on another vehicle

jsprit-core/src/main/java/com/graphhopper/jsprit/core/problem/vehicle/VehicleImpl.java

@@ -330,6 +330,16 @@ public class VehicleImpl extends AbstractVehicle {
         }
     }
 
+    /**
+     * Returns a simple copy of vehicle.
+     *
+     * @param vehicle
+     * @return
+     */
+    public static Vehicle copyOf(Vehicle vehicle) {
+        return VehicleImpl.Builder.newInstance(vehicle).build();
+    }
+
     /**
      * Returns empty/noVehicle which is a vehicle having no capacity, no type and no reasonable id.
      * <p>