svtplay_dl.output: Make progress() wrap progressbar()
svtplay_dl.output: Make progress() wrap progressbar()

The progressbar() currently does not handle the case where the total size is
unknown. But with this change, progress() will internally use progressbar()
for its bar generation, while still supporting a more basic progress info when
total size is unknown.

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