ALPN Support for netty

Motivation:

Netty currently only leveraged npn-api and npn-boot. It does not leverage the alpn-api and alpn-boot packages for
ALPN support.  ALPN is needed to be compliant with the HTTP/2 spec.

Modifications:

-SslContext and JdkSslContext to support ALPN
-JettyNpn* class restructure for NPN and ALPN common aspects

Result:
-Netty supports ALPN and NPN
I had to add the ALPN entry in here to avoid getting a build error (as described in the PR comments).  I must admit I am confused why NPN worked before this, and so there is likely another way to solve this.  Who would know about this type of thing?  Is it possible the jetty ALPN pom is not exporting correctly?