Add versioning

[maximiliani]

• two modes: 'released' and 'in development'
• when 'released'
  • no modifications/deletion allowed
  • reference to earlier and next versions
  • each version has own PID
  • store JSON in Handle record for persistence
• when 'in development'
  • @Version for optimistic locking
  • modifications possible at no notice
  • PID refers to latest version

[maximiliani]

This could be done with: https://docs.spring.io/spring-statemachine/docs/3.2.1/reference/