Support segmented images
Issue proposed by @NielsRogge 

eg https://huggingface.co/datasets/scene_parse_150

<img width="785" alt="Capture d’écran 2022-03-04 à 10 56 05" src="https://user-images.githubusercontent.com/1676121/156741519-fbae6844-2606-4c28-837e-279d83d00865.png">

Every pixel in the images of the `annotation` column has a value that gives its class, and the dataset itself is associated with a color palette (eg https://github.com/open-mmlab/mmsegmentation/blob/98a353b674c6052d319e7de4e5bcd65d670fcf84/mmseg/datasets/ade.py#L47) that maps every class with a color.

So we might want to render the image as a colored image instead of a black and white one.

cc @mariosasko: how could I get the color palette information after `load_dataset()`? Is it managed by the `datasets` library?

Support segmented images: Issue proposed by @NielsRogge 

eg https://huggingface.co/datasets/scene_parse_150

<img width="785" alt="Capture d’écran 2022-03-04 à 10 56 05" src="https://user-images.githubusercontent.com/1676121/156741519-fbae6844-2606-4c28-837e-279d83d00865.png">

Every pixel in the images of the `annotation` column has a value that gives its class, and the dataset itself is associated with a color palette (eg https://github.com/open-mmlab/mmsegmentation/blob/98a353b674c6052d319e7de4e5bcd65d670fcf84/mmseg/datasets/ade.py#L47) that maps every class with a color.

So we might want to render the image as a colored image instead of a black and white one.

cc @mariosasko: how could I get the color palette information after `load_dataset()`? Is it managed by the `datasets` library?
