Fail SSL Handshake if no supported Application Protocols

Motiviation:
jetty-alpn does not support the no_application_protocol alert as defined in http://tools.ietf.org/html/rfc7301#section-3.2.  This should be supported to fail the handshake if there are no supported protocols found.

Modifications:
-Allow ALPN.ServerProvider.select to return null.
-ALPN.ServerProvider.select will be handled by ServerHandshaker.java as a fatal handshake error
-Add an Alerts.java to provide the missing alert_no_application_protocol definition
-Add unit tests to test this case

Result:
-jetty-boot supports no_application_protocol alert as defined in http://tools.ietf.org/html/rfc7301#section-3.2