Extract event dispatching out of REST forwarder

Event dispatching was done in the EventRestApiServlet. There are a few
reasons why this is needed:

- it can be reused by other forwarder implementation
- simplify the classes and the unit tests
- it can be reused by any new feature that needs to dispatch an event
without forwarding it to the other node

Change-Id: Ib819a42ee8b4e200959044e59c527fa42b06ac1d
4 files changed