Use @API annotation for marking supported and unsupported features

[Crumby]

In order to be able to distinguish between supported and unsupported features we should use @API annotation on test classes. This way we would be able to say which features can user expect to be supported with backward compatibility support, which are experimental or which are internal and not meant to be use by other parties then within project itself.

See http://junit.org/junit5/docs/current/user-guide/#api-evolution for example.

[Crumby]

Closing as out of date.