Event callback implementation.

* Rename _imei property by _identity.
* Event callback implementation. More events comming soon.
  - onConnect
  - onDisconnect
  - onLogin
  - onSendNickname
  - onSendPresence
  - onPing
  - onPong
  - onDissectPhone
  - onFailedDissectPhone
  - onGoodCredentials
  - onBadCredentials
* Add disconnect function.
* New message id implementation.
* Change dissectPhone function to protected.