Add "view image metadata" option

[holgerhennig]

Navigate to: classifier

Feature request: Currently, right-click on an image opens a menu with several options (Select, Deselect etc). Add menu entry: view image metadata. Clicking on view image metadata then shows metadata (image no, path, filename etc.). The information appears in the logfile window when fetching an image. But when you fetch 50 images and you want the metainformation for image #32, then searching through the logfile is cumbersome and prone to errors.