Add watcher mode

- The watcher mode disables most interface elements (head/footer/etc)
  is is meant as a watch only mode to embed in webpages
- New GET parameter *watcher* enables watcher mode
- CLIENT has a new attribute watcherMode (false by default)
- In watcher moder
  * Notificatiosn are disabled
  * The footer is never showed
  * The header is hidden on start
  * Instead of opening the settings panel on start we
    just show an event message if the url is missing