[NUI] Clean up DisconnectFromSignals(). and Add Exception when Animation is used...

[NUI] Clean up DisconnectFromSignals(). and Add Exception when Animation is used after disposed

- Add Exception when Animation's method or property is used after itself has been disposed already. (requested by GBM)
- All NUI object will throw an ObjectDisposedException when it is tried to be used after disposed.
- BaseHandle's internal SwigCPtr has setter and getter, but setter seems to be dangerous so it is changed to be getter only. (requested by GBM)
- SwigCPtr becomes only getter, so DisconnectFromSignals() has been changed accordingly.