Support shoutcast streams

ffprobe/raw-file support already mostly handles this, except the duration is reported as NaN which busts the playlist metadata.

Example data:

$ ffprobe -of json -show_format -show_streams https://streaming-ent.shoutcast.com/foxnews
ffprobe version 3.3.6 Copyright (c) 2007-2017 the FFmpeg developers
  built with gcc 7.3.0 (Gentoo 7.3.0-r3 p1.4)
  configuration: --prefix=/usr --libdir=/usr/lib64 --shlibdir=/usr/lib64 --docdir=/usr/share/doc/ffmpeg-3.3.6/html --mandir=/usr/share/man --enable-shared --cc=x86_64-pc-linux-gnu-gcc --cxx=x86_64-pc-linux-gnu-g++ --ar=x86_64-pc-linux-gnu-ar --optflags='-O2 -pipe -march=native' --disable-static --enable-avfilter --enable-avresample --disable-stripping --disable-libcelt --disable-indev=v4l2 --disable-outdev=v4l2 --disable-indev=oss --disable-indev=jack --disable-outdev=oss --enable-bzlib --disable-runtime-cpudetect --disable-debug --disable-gcrypt --enable-gnutls --disable-gmp --enable-gpl --enable-hardcoded-tables --enable-iconv --disable-lzma --enable-network --disable-openssl --enable-postproc --disable-libsmbclient --enable-ffplay --enable-sdl2 --disable-vaapi --disable-vdpau --enable-xlib --enable-libxcb --enable-libxcb-shm --enable-libxcb-xfixes --enable-zlib --disable-libcdio --disable-libiec61883 --disable-libdc1394 --enable-libcaca --disable-openal --enable-opengl --disable-libv4l2 --enable-libpulse --disable-libopencore-amrwb --disable-libopencore-amrnb --disable-libfdk-aac --disable-libopenjpeg --disable-libbluray --disable-libgme --disable-libgsm --disable-mmal --disable-libmodplug --enable-libopus --disable-libilbc --enable-librtmp --disable-libssh --disable-libschroedinger --disable-libspeex --enable-libvorbis --enable-libvpx --disable-libzvbi --disable-libbs2b --disable-chromaprint --disable-libflite --disable-frei0r --disable-libfribidi --disable-fontconfig --disable-ladspa --enable-libass --enable-libfreetype --disable-librubberband --disable-netcdf --disable-libzmq --disable-libzimg --disable-libsoxr --enable-pthreads --disable-libvo-amrwbenc --enable-libmp3lame --disable-libkvazaar --disable-nvenc --disable-libopenh264 --disable-libsnappy --enable-libtheora --disable-libtwolame --disable-libwavpack --disable-libwebp --enable-libx264 --disable-libx265 --enable-libxvid --disable-amd3dnow --disable-amd3dnowext --disable-fma4 --disable-xop --cpu=host --disable-doc --disable-htmlpages --enable-manpages
  libavutil      55. 58.100 / 55. 58.100
  libavcodec     57. 89.100 / 57. 89.100
  libavformat    57. 71.100 / 57. 71.100
  libavdevice    57.  6.100 / 57.  6.100
  libavfilter     6. 82.100 /  6. 82.100
  libavresample   3.  5.  0 /  3.  5.  0
  libswscale      4.  6.100 /  4.  6.100
  libswresample   2.  7.100 /  2.  7.100
  libpostproc    54.  5.100 / 54.  5.100
{
Input #0, mp3, from 'https://streaming-ent.shoutcast.com/foxnews':
  Metadata:
    icy-br          : 96
    icy-description : FOX News Radio
    icy-genre       : News & Talk 
    icy-name        : FOX News Radio
    icy-pub         : 1
  Duration: N/A, start: 0.000000, bitrate: 96 kb/s
    Stream #0:0: Audio: mp3, 44100 Hz, stereo, s16p, 96 kb/s
    "streams": [
        {
            "index": 0,
            "codec_name": "mp3",
            "codec_long_name": "MP3 (MPEG audio layer 3)",
            "codec_type": "audio",
            "codec_time_base": "1/44100",
            "codec_tag_string": "[0][0][0][0]",
            "codec_tag": "0x0000",
            "sample_fmt": "s16p",
            "sample_rate": "44100",
            "channels": 2,
            "channel_layout": "stereo",
            "bits_per_sample": 0,
            "r_frame_rate": "0/0",
            "avg_frame_rate": "0/0",
            "time_base": "1/14112000",
            "start_pts": 0,
            "start_time": "0.000000",
            "bit_rate": "96000",
            "disposition": {
                "default": 0,
                "dub": 0,
                "original": 0,
                "comment": 0,
                "lyrics": 0,
                "karaoke": 0,
                "forced": 0,
                "hearing_impaired": 0,
                "visual_impaired": 0,
                "clean_effects": 0,
                "attached_pic": 0,
                "timed_thumbnails": 0
            }
        }
    ],
    "format": {
        "filename": "https://streaming-ent.shoutcast.com/foxnews",
        "nb_streams": 1,
        "nb_programs": 0,
        "format_name": "mp3",
        "format_long_name": "MP2/3 (MPEG audio layer 2/3)",
        "start_time": "0.000000",
        "bit_rate": "96000",
        "probe_score": 51,
        "tags": {
            "icy-br": "96",
            "icy-description": "FOX News Radio",
            "icy-genre": "News & Talk ",
            "icy-name": "FOX News Radio",
            "icy-pub": "1"
        }
    }
}

In order to resolve this, CyTube should:

Detect that it's a shoutcast stream by the presence of the icy headers (present in "tags" in the ffprobe output)
Read the title out of the icy-name tag
Report the duration as 0 as is standard for other live types

More generally, CyTube should validate all returned metadata to avoid corrupting a playlist with NaN durations (this is now the second reported instance of this happening).

calzoneman / sync

Support shoutcast streams #785