replace twitch player with div when switching to youtube video

swfobject which is used to embed the twitch flash player replaces an empty
div-tag. So when removing the twitch player, we need to add the empty div-tag.
That's done by replacing the node. Otherwise it isn't possible to embed the
twitch player again.
use local version of logo instead of dropbox
added playlist support to twitch videos

Twitch doesn't support playlists like youtube. There are now simple Next and
Previous buttons to switch videos.