Put labels and features in separate files with CNTKTextFormatReader

Use the composite reader to specifiy the two files, one for lables, and one for features. And make sure to match sequence id's in labels file and the features file.

reader = [
  …
  deserializers = (
  [
      type = "CNTKTextFormatDeserializer" ; module = "CNTKTextFormatReader"
      file = "$RootDir$/features.txt"
      input = [ features = [...]]
  ]:[
      type = "CNTKTextFormatDeserializer" ; module = "CNTKTextFormatReader"
      file = "$RootDir$/labels.txt"
      input = [ labels = [...]]
  ]
]