Correct language cookie path

[johanjanssens]

The current implementation in plugins/system/languagefilter fails to correctly set the cookie path. This results in multiple language cookies for different paths.

For example, if you enable languages and add a few submenu items, you will see that a language cookie is being set on every sublevel. See this screenshot:

Use the basepath for each application (site|admin) so the language cookie is managed only once per app.

Example:

https://github.com/nooku/nooku-framework/blob/master/code/libraries/koowa/libraries/dispatcher/authenticator/csrf.php#L125