config: reorganize configuration file

  config.server.port
  channels -> config.channels
providers: add a simple http provider

  The simple-http provider is used in the sample config file to re-stream an
  existing VLC channel using another name. This is not very usefull, but this
  provider could also be used to "chain" node-iptv-proxy instances, or simply
  stream a pre-recorded file hosted on a static http server.

  Actually, it can stream anything that can be accessed using a static http URL