Add filtering support on ServiceRegistry

[jbonofre]

It's possible to register several services with the same class in the ServiceRegistry.
In that case, it would be great to extend the service registry with a service key/name, and be able to do serviceRegistry.get("key", MyInterface.class).

[fpapon]

Do we want to add properties associate to the key to be able to perform some fine search in the service registry? Like we can have with the SCR of OSGi.