router: Added X-Request-Id header to requests sent to backends.
router: Added tests to verify X-Forwarded-For will append existing X-Forwarded-For header from the client.
Closes #66.

Signed-off-by: Ian Neubert <ian@ianneubert.com>
Merge pull request #117 from ianneub/x_request_id

router: Added X-Request-Id header to close #66