further simplify our in-app settings implementation and solve the remaining issue with the subtitle encoding setting (close #8679)

http file downloader: add a proper class taking care of this and use the circular progress indicator for visualization in the popover

menu: get rid of the http server info button and show the address to upload stuff directly in a label

drop the dialogs to open URLs with a text field, which is prefilled if we believe that a valid URL is on the pasteboard

proper design still to do