Need to suggest a name for saved .png files

[David Planella]

Right now, when saving a QR code as an image using the Save button, we don't suggest a name, so we expect the user to know that they need to add the .png extension.

We should not do that. Instead, we should add a placeholder filename (perhaps with a timestamp, similarly to what the PrintScr key does when capturing screenshots of the system) and mark it as translatable.