Add unload event handling to ClientNetworkManager (#137)

Added a new method `onWorldUnload` to `ClientNetworkManager` to destroy and clear any network instances when the world event `Unload` is triggered. The addition of this event handler was necessary to prevent the possibility of any network instances persisting on the client side beyond the World lifetime, thus potentially causing memory leaks.

src/main/java/crazypants/enderio/machine/capbank/network/ClientNetworkManager.java

@@ -4,13 +4,20 @@
 import java.util.Map;
 
 import net.minecraft.world.World;
+import net.minecraftforge.common.MinecraftForge;
+import net.minecraftforge.event.world.WorldEvent;
 
+import cpw.mods.fml.common.eventhandler.SubscribeEvent;
 import crazypants.enderio.machine.capbank.TileCapBank;
 
 public class ClientNetworkManager {
 
     private static final ClientNetworkManager instance = new ClientNetworkManager();
 
+    static {
+        MinecraftForge.EVENT_BUS.register(instance);
+    }
+
     public static ClientNetworkManager getInstance() {
         return instance;
     }
@@ -53,4 +60,12 @@ public void addToNetwork(int id, TileCapBank tileCapBank) {
         CapBankClientNetwork network = getOrCreateNetwork(id);
         network.addMember(tileCapBank);
     }
+
+    @SubscribeEvent
+    public void onWorldUnload(WorldEvent.Unload event) {
+        if (event.world.isRemote) {
+            networks.forEach((id, network) -> network.destroyNetwork());
+            networks.clear();
+        }
+    }
 }