Find plugins in controller

        :param plugin_name: Name of the plugin to find
        :type plugin_name: str | None
        :return: Plugin or None and error message
        :rtype: (settable_plugin.SettablePlugin | None, str)

def _plugin_get(self, plugin_name):
        """
        Find plugins in controller

        :param plugin_name: Name of the plugin to find
        :type plugin_name: str | None
        :return: Plugin or None and error message
        :rtype: (settable_plugin.SettablePlugin | None, str)
        """
        if not plugin_name:
            return None, u"Plugin name not set"
        for plugin in self.controller.plugins:
            if not isinstance(plugin, SettablePlugin):
                continue
            if plugin.name == plugin_name:
                return plugin, ""
        return None, u"Settable plugin '{}' not found".format(plugin_name)