Recreate the Core service

[jrobinAV]

After the Core service is replaced by the Orchestrator service, we want to keep the Core service compatible between 3.X and 4.Y. The motivation is to give time to the developers to implement the changes and help them understand how to remain compatible.

• Recreate the Core service class as a proxy to the orchestrator service class.
• Implement just a deprecation message saying the Core service does not exist anymore.