Initial refactoring of the ServerSentServlet and ServerEventSource.

Still uses 'Object' as the input, and ofType to differentiate. Not ideal.
More refactoring and cleaning.

- Reformatted some classes and removed warnings.
- Removed now redundant 'OnSubscribe' implementation.
- Moved classes and removed the vaguely named 'reactive' package.
- Removed old Runner class.
- Unified App class to take 'test-data' when no serial ports available.
- Removed 'static' access to Responder.
- Removed 'configuration' package as we did not get around to using it.