Future compatibility with TLS ALPN

Motivation:

According to TLS ALPN draft-05, a client sends the list of the supported
protocols and a server responds with the selected protocol, which is
different from NPN.  Therefore, ApplicationProtocolSelector won't work
with ALPN

Modifications:

- Use Iterable<String> to list the supported protocols on the client
  side, rather than using ApplicationProtocolSelector
- Remove ApplicationProtocolSelector

Result:

Future compatibility with TLS ALPN