Public / private module separation

We need a better separation of SPI / interfaces and implementation classes. That's a requisite for stating what is meant to comply with strict backward compatibility rules (and hence needs to go through proper deprecation path before removal, etc.) and what is private (and hence can be changed at any time, usually without affecting final user applications).
When it comes to integrating with WildFly / EAP, only the components including spi and interfaces would end up into public modules, everything else should live into modules marked as private.