Made server close when core is destroyed

core/src/io/anuke/mindustry/net/Packets.java

@@ -135,4 +135,8 @@ public class Packets {
     public static class EntityRequestPacket{
         public int id;
     }
+
+    public static class GameOverPacket{
+
+    }
 }

core/src/io/anuke/mindustry/net/Registrator.java

@@ -38,6 +38,7 @@ public class Registrator {
                 BlockConfigPacket.class,
                 EntityRequestPacket.class,
                 ConnectConfirmPacket.class,
+                GameOverPacket.class,
 
                 Class.class,
                 byte[].class,