Separate Interfaces from Classes

[amihaiemil]

All the classes should be in their own package, for Access Control reasons. However, we can separate the interfaces from the classes. Let's try to do this without breaking backwards compatibility.

We can leave the interfaces in the current package and create an impl package for the classes.

[irinil]

Should be this mentioned in the JavaDocs too?

[amihaiemil]

@irinil If you want to continue contributing, I would start with other tickets, until you learn the library's architecture. For instance, the ticket about continuing with the Swarm API.

See how other API endpoints are implemented :)