Unbind proxy events when presenter.unbind() is called

The change was a bit more complex than I first expected. I explain: As per the presenter's documentation, if Presenter.unbind() is called, then Presenter.bind() must be called in order to rebind the presenter ; which means the presenter is not necessarily released by the client-application and can be manually reattached. So if I unbind the proxy when the presenter's unbind() is called, I must perform the same task for bind()...

Now I tried to hide this logic in the proxy with an inner class so custom proxies do not accidentally override/call these methods. This logic can be discussed though...