Online ML AI engine

Pull request #5: Dev

Merge in EOSC-RS/online-ml-ai-engine from dev to master

* commit 'ffa0f4cf4223076c440ae437b36eca099dc8fcb5':
  Add shuffle popular resources
  aai_uid is not specified in the request if it is "" instead of none
  Sorting resources when no candidate is present in the database