This change shows theme icons on the "Open With..." button (the standard "document-open" icon) and on the "Open with 'application'" button (the application's icon as defined in its service file). These buttons previously had no icons, but the other two in the dialogue did so unbalancing the appearance.
The dialogue text is converted to KUIT markup.
This requires passing the service 'offer' to AttachmentDialog::AttachmentDialog(), instead of the application name.