image uploader should not accept other file types than image files

Parent: [EPIC] Extend Show Management Area and improve ... (#149 - closed)

During the COMMIT radio tech meeting on 20/11/23 we tried some things with the uploader interface and found out that the image uploader does not warn or prevent users to load a file which is not an image. The audio uploader also does not warn, but aborts the upload immediately (because of ffmpeg errors)

This can be a potential security risk and it is a lack in terms of UI/UX quality management (because it can happen that users make mistakes). It would be great to offer an info on allowed file types in the basic uploader UI and give a warning, in case a user does try to upload another file type.