[DATAFARI-337] Warn user that he has been disconnected

Currently, a connected user (searchexpert or searchadmin) is silently disconnected after a timeout. This means that he can still navigate through parts of the admin UI, and even fill in certain fields. He can also trigger some actions, but they will silently fail as he actually is disconnected. Instead, as soon as a user is disconnected, at best he is kicked out of the admin page, at worse he gets a popup whenever he tries to do anything in the admin ui.

Issue metadata

Issue type: Amélioration
Priority: Medium
Fix versions: Datafari 4.2