Implementing INetlet

Our class wants to be a netlet, so it must implement the INetlet interface. Every method in the class is actually part of INetlet or one of its super-classes, so this really is the smallest netlet we could write.

Of course a netlet is more than just a single class. Clearly we also need some classes and interfaces from org.jtrix.base and also NullService in Libjtrix. But it's this class which communicates with the node: when the netlet starts, it starts here; when the netlet stops it's this class which finds out first; and in general if there's any node/netlet communication this is where it takes place.