Provide SSLOptions to allow updates of the certificate of a TCP server or client

[vietj]

Provides support for reloading of a TCP server or client, a new SSLOptions class has been introducing which captures the reloadable part of the current configuration.

Reconfiguration is explicit and requires a call to a new updateSSLOptions method that loads and validates the configuration and then updates the SSL context when it succeeds.

vertx.setPeriodic(REFRESH_PERIOD, id -> {
  Optional<SSLOptions> options = refreshUpdatedConfiguration();
  if (options.isPresent()) {
    Future<Void> fut = server.updateSSLOptions(options.get());
  }
});