Add startable, stopable, destroyable interface for registry

[sbernard31]

In Leshan Server, we have some crapy code

 // start client registry
if (clientRegistry instanceof ClientRegistryImpl) {
     ((ClientRegistryImpl) clientRegistry).start();
}

Maybe, a good way to remove this kind of code is to propose 3 interface Startable, Stopable and Destroyable, which could be implemented by registries if needed. LeshanServer could start, stop or/and destroy it when needed.

[sbernard31]

Integrated in master