Improve design of CaseService

[jonenst]

• Do you want to request a feature or report a bug?
  Bug

• What is the current behavior?
  Case service has a weird design. It has a setFileSystem method that is used only for tests. It takes somes dependencies from spring, other not from spring. It checks the filesystem at every request but this should be done only once when the bean is initialized. (right now it can't be done in @PostConstruct by spring because tests initialize the filesystem after that)

• What is the expected behavior?
  Simpler design, proper initialization

• What is the motivation / use case for changing the behavior?
  Maintainability