add http-stream support, URL is hardcoded for now

[parabelboi]

hi notandy, the stream url is still hardcoded to some http://mpd:8000/mpd.ogg dont know whether mpd can provide this info on the other hand: maybe better to make the stream URL configurable on the client side: if mpd also streams to a broadcaster, one wants to check whether the stream is "on air" too.

[mgaunard]

This should either be an option on the command line or in the browser

[mgaunard]

I tested this with Chrome, it appears that the local volume slider doesn't work.

[SuperBFG7]

For my updated version that tries to derive the stream url, stores it in a cookie and makes it configurable see: https://github.com/SuperBFG7/ympd/tree/local_play