More robust grouped? detection

We now just check if the slide belongs to UnGroup, ie. group for ungrouped slides
Less sql-intesive grouped check

We now utilize the current_event helper to avoid a sql query per slide rendered.
Display state on the UI

We now display the new status information in the UI and style the display items based on it.
Better handling of the displays current image

We now use a static error image when the displays status in unknown or erroneous.