viaplay: support for wsrt (vtt) subtitle
viaplay: support for wsrt (vtt) subtitle

fixes: #501

olof/svtplay-dl,spaam/svtplay-dl,selepo/svtplay-dl,qnorsten/svtplay-dl,dalgr/svtplay-dl,selepo/svtplay-dl,iwconfig/svtplay-dl,olof/svtplay-dl,spaam/svtplay-dl,dalgr/svtplay-dl,iwconfig/svtplay-dl,qnorsten/svtplay-dl