code: function (pluginName, program, applicationServer, callback) {
      var config = configHelpers.getConfig();
  
      // Test if plugin is installed.
      if (config.plugins[pluginName] === undefined) {
        logger.error('Plugin ' + pluginName + ' not installed!');
        nodeHelpers.invoke(callback);
  
      } else {
  
        try {
  
          // Load plugin
          if (pluginHelpers.loadedPlugins[pluginName] === undefined) {
            pluginHelpers.loadPlugin(pluginName, program);
          }
          var plugin = pluginHelpers.loadedPlugins[pluginName];
  
          if (plugin !== null) {
            pluginHelpers.startedPlugins[plugin] = true;
  
            if (plugin.configureAppServer && applicationServer) {
              logger.info('Configuring plugin ' + pluginName + '...');
  
              plugin.configureAppServer(
                applicationServer, config, routes, function logResult () {
  
                logger.info('Plugin ' + pluginName + ' configured.');
                nodeHelpers.invoke(callback);
              });
  
            // Plugin has no action to perform on the server.
            } else {
              nodeHelpers.invoke(callback);
            }
  
          // Something went wrong while loading the plugin.
          } else {
            logger.error('Plugin ' + pluginName + ' was not properly loaded!');
            nodeHelpers.invoke(callback);
          }
  
        } catch(err) {
          logger.raw(err);
          logger.error('Plugin ' + pluginName + ' loading failed.');
          nodeHelpers.invoke(callback, err);
        }
      }
    }
docs: Start given plugin (require it, run configuration and apply change to
  cozy light server).
  NB: Do not load given plugin if it is disabled.
  
  @param pluginName The plugin name to start.
  @param program The commander program to bind.
  @param applicationServer The application server to connect the plugin on.
  @param callback Termination.