improve support for embed url-arguments

[xDashh]

As discussed on Discord.
E.g. https://strims.gg/youtube-playlist/PLJbWNarT9D8msO9D8p3nvq7Wj9FBQvvkC&index=41
works, notice the index= with & (not ?) probably coincidentally, however the amount of viewers is not counted probably because there are problems with using the "incurrent" URL internally...

Links like these should work as expected (counting viewers, also the same "trick" with a t= parameter for normal yt embeds breaks the embed) and probably count towards viewers on the version with the index= parameter (i.e. normalize the url for keeping track). it would be nice though to keep supporting adding paramters for the embed-url, like youtube-start-time parameter (t=).