Comment 1 for bug 714198

Added a general event listener mechansim.
Currently, you can only subscribe to the performImport event.

Additional, event support is provided in later versions. However this is quite simple:

- Just annotate a method / function with the developed @Observable annotation.
- Create a event class in datafinder.core.events.
- Add a specific constant and extend the _eventMap in datafinder.script_api.events