GameEvent must be Copyable

Error:
```
java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextNode(HashMap.java:1445)
at java.util.HashMap$EntryIterator.next(HashMap.java:1479)
at java.util.HashMap$EntryIterator.next(HashMap.java:1477)
at mage.game.GameState.(GameState.java:190)
at mage.game.GameState.copy(GameState.java:299)
at mage.game.GameImpl.rollbackTurnsExecution(GameImpl.java:3695)
at mage.game.GameImpl.playTurn(GameImpl.java:1078)
at mage.game.GameImpl.play(GameImpl.java:997)
at mage.game.GameImpl.start(GameImpl.java:973)
at mage.server.game.GameWorker.call(GameWorker.java:34)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
```

Possible reason:
* Some `GameEvent` implementations uses game objects and it's share between states/rollbacks/simulations -- it's a buggy and must be fixed by `Copyable` implementation and fixed GameState copy constructor