Create messaging concept

[mmacata]

As more an more plugins are developed, it is not feasable to differ between them only by using another endpoint. This current approach makes it hard to chain different plugins and is not very flexible.
The task here should be to come up with a concept which allows different plugins to be chained. Message queue / broker could be a cool approach with redis already needed by actinia and job queue already possible via redis.
The concept should be flexible, so that the "chain" works, even though not all plugins are always installed.