Wrong config calls for cookie settings in languagefilter and logout plugin

This PR fixes two issues related to cookie settings in global configuration
- The languagefilter and logout plugins were looking for the config parameters `config.cookie_domain` and `config.cookie_path`. The correct call is without the `config.` part.
- There were some places where the `cookie_path` parameter didn't fetch the correct default value `/`. Together with SEF turned on, this could result in cookies only being valid for a submenu of the page since the path was taken from the current URL instead from root.