Make ConnectionFactory easier to use

Related to #330.

Many settings have been added to ConnectionFactory over the years, making it somewhat harder to configure. It's for instance easy to omit an important option when setting TLS, because the different TLS-related options are scattered: ConnectionFactory#useSslProtocol, ConnectionFactory#setSslContextFactory, ConnectionFactory#enableHostnameVerification. Same thing for NIO (mitigated by NioParams).

A more "use-case oriented", less JavaBeans-like way could improve the situation, e.g.:

cf.nio().executor(myNioExecutor).socketChannelConfigurator(configurator) // NIO configuration
  .connectionFactory() // going back to the connection factory (call may be avoided with syntax trick)
  .tls().context(sslContext).hostnameVerification(true); // TLS configuration

Not longer useful configuration methods would be deprecated and scheduled for removal in 7.0.0.