New Core Event PRE_SEND_RESPONSE (#477, #386).

Fired before the response is send to the client. That is exactly once per request.
This allows plugins to set certain response headers like `Last-Modified`.

New listener interface:
    de.deepamehta.core.service.event.PreSendResponseListener
Listener method:
    void preSendResponse(ContainerResponse response)

Note: ContainerResponse is a Jersey-specific class (com.sun.jersey.spi.container.ContainerResponse).
We should remove the Jersey dependency and move to JAX-RS 2.0 instead.

See ticket 477.
See ticket 386.