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