Navigation portlet: css-classes for workflow state and expiration

This PR adds two classes to items in the navigation:

1. A `state-*` class with the workflow state (e.g. `state-private`)
2. A `content-expired` class when the content is expired

This allows to highlight contents in a specific state (e.g. private or submitted) or expired content for editors.
There is no CSS styling those classes, the CSS belongs into integration packages..