Fixed JERSEY-1527, JERSEY-1528, JERSEY-1531.

- Returning null response results in HTTP 204.
- Response with no status is either send as 200 (with entity) or 204 (without entity).
- Added test to verify that inbound client response can be send as outbound server response.

Change-Id: I53dd304cb5fb946820a5ca242b823a8ff1d67e0a
Signed-off-by: Marek Potociar <marek.potociar@oracle.com>