Idempotent services

[jan-gerling]

Implements idempotent commands for order, user and stock services as required for SAGAS.

• implemented push put buffer based on hashmap and simple push out buffer
• added optional parameter operationId: Long to all non idempotent to one routes in order, user and stock services
• added operation id to events
• added operation id to commands
• extended persistent actor base to handle already done commands and send immediate responds if cached