Events have not good implementations of equals(), hashCode() and toString()

Many events have neither of the three and a `toString()` call is for example handled by `PlayerEvent` class, which prints `PlayerEvent` and not the actual event subclass. Additionally `CancellablePlayerEvent` and `InventoryTransactionEvent` as examples are ignoring fields from its super class in its `toString()`.

I suggest removing custom equals and hashCode implementations from events as there is no reason to save and compare event instances.

Also toString() methods should be updated and added to all events to include super class fields like player or entity and cancelled.