[WIP] Notification support

[geofjamg]

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

• What is the current behavior?
  When a new case is available there is no way to be notified and for instance start a workflow from this case.

• What is the expected behavior?
  We have to think about an architecture that would allow workflows to wait for new case to be available. We could imagine a broker based architecture that will be used to send notification when a new case is added (either directly to the file system or through the REST API).

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

• Please tell us about your environment:

  • PowSyBl Version: ...
  • OS Version: ...

• Other information (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, spectrum, etc)

(if a question doesn't apply, you can delete it)