New feature: System for dispatching/listening to events sent thorugh non-related classes

[alfongj]

As there are many classes in the current project, and most of them aren't directly related to one another, custom events can't be transmitted in many scenarios without an EventDispatcher that is able to work on all classes.

Therefore, a new singleton class that manages the dispatching and listening to events to any class who has an instance of it, is needed to solve the problem cleanly.

[alfongj]

The solution consists in 2 classes: util.EventManager (which is a class that extends from EventDispatcher giving it the structure of a Singleton) ad util.EvCodes which acts as an Enum for defining custom event codes.