docs: def load_plugins():
      """Loads all plugins specified in the RAFCON_PLUGIN_PATH environment variable
      """
      plugins = os.environ.get('RAFCON_PLUGIN_PATH', '')
      plugin_list = set(plugins.split(os.pathsep))
      global plugin_dict
      for plugin_path in plugin_list:
          if not plugin_path:
              continue
          plugin_path = os.path.expandvars(os.path.expanduser(plugin_path)).strip()
          if not os.path.exists(plugin_path):
              logger.error("The specified plugin path does not exist: {}".format(plugin_path))
              continue
          dir_name, plugin_name = os.path.split(plugin_path.rstrip('/'))
          logger.info("Found plugin '{}' at {}".format(plugin_name, plugin_path))
          sys.path.insert(0, dir_name)
          if plugin_name in plugin_dict:
              logger.error("Plugin '{}' already loaded".format(plugin_name))
          else:
              try:
                  module = importlib.import_module(plugin_name)
                  plugin_dict[plugin_name] = module
                  logger.info("Successfully loaded plugin '{}'".format(plugin_name))
              except ImportError as e:
                  logger.error("Could not import plugin '{}': {}\n{}".format(plugin_name, e, str(traceback.format_exc())))