OPAL-1601: Use DisclosurePanel instead of custom one...

Is it ok ?

![image](https://f.cloud.github.com/assets/2565497/132788/c54bf84a-7093-11e2-8089-95b8197cbb06.png)

![image](https://f.cloud.github.com/assets/2565497/132789/cfc08f98-7093-11e2-84e9-6d38e995ef4b.png)