implement workload deletion

[alexandrebrg]

What needs to be done ?

• [x] Controller handling of a workload deletion
  • [x] Entry must be deleted from database
  • [x] Related instances must be deleted from database
• [x] Ensure riklet function deletion handling is complete
  • [ ] Instance deletion should delete file related to the instance
  • [ ] To be discussed: when and how to handle workload cache deletion
• [ ] Full deletion handling of instances of a workload in scheduler

Why it needs to be done ?

• Dependent project Morty needs to be able to delete workloads