Refactoring project structure for Leelo

[Tommaso Teofili]

Hi all,
I've created https://issues.apache.org/jira/browse/AMBER-10 to track project
structure change, as discussed before.
I'll move on with that change and leave the oauth-2.0 directory empty for
the upcoming Leelo inclusion (any more news on that?).
Cheers,
Tommaso