Add UNIOS loader

[bbutkovic]

This PR adds support for Radio UNIOS

Unfortunately, the AJAX call from frontend is a JSONP request meaning we had to strip out the function call part and then parse the JSON.

JSONP Response example from http://radio.unios.hr:8000/json.xsl

Response (prettified):

parseMusic(
  {
    "/fm.mp3": {
      "server_name": "fm.mp3",
      "listeners": "1",
      "description": "Radio UNIOS FM",
      "title": "Jimi Hendrix - Little Wing",
      "genre": "Misc",
      "bitrate": "192",
      "url": "radio.unios.hr"
    },
    ...
  }
);

The JSON contains different streams, after some digging I found that we are interested in the "/fm.mp3" handle for the actual stream that is broadcasted on 107.8 MHz in Osijek.