title: slf4j, logback - refer to appender that is not referenced from any logger
body: <p>I want to define SMTPAppender in the logger.xml file, but I do not wish to reference it from any logger. </p>
  
  <p>Then when my application loads, I wish to programmatically add this appender to specific loggers. </p>
  
  <p>However the "getAppender" method is accessible only from Logger. </p>
  
  <p>Is there a way to work around this and get the appender without going through any logger?</p>