Separate command to download images

We need a new command and to update the current teklia-dan dataset extract

Specification

teklia-dan dataset extract

• Same as before (without image downloading)
• Generate a file split.json will look like

{
    "train": {
        "<path_to_image>": {
            "text": "...",
            "url": "<download_url>",
        }
    },
    ...
}

teklia-dan dataset download

• split.json lists the images that need to be downloaded.
• labels.json lists the images already downloaded

• Takes a split.json
• Takes a path to labels.json, optional. If present, load data
• Iterate over split, and over image paths
• Try downloading through URL with multithreading
  • if successful do
    • remove from split.json data
    • add to labels.json data
• Save labels.json data

{
    "train": {
        "<path_to_image>": "<transcription>"
    }
}

• Save split.json data