Add image quality Assessment

[matkoniecz]

it may desirable to have ability to check whatever image is https://commons.wikimedia.org/wiki/Commons:Quality_images or https://commons.wikimedia.org/wiki/Commons:Featured_pictures

For example in my case I want to select single image from multiple articles, so it is preferable to select one marked as high-quality rather than random one

[siznax]

Thanks for opening an issue @matkoniecz!

It looks like API:Imageinfo offers Assessment info with iiprop=extmetadata:

File:Gull portrait ca usa.jpg: https://commons.wikimedia.org/w/api.php?action=query&titles=File:Gull%20portrait%20ca%20usa.jpg&prop=imageinfo&iiprop=metadata|commonmetadata|extmetadata

"extmetadata": {
    "Assessments": {
        "value": "featured|poty|potd|quality",
        "source": "commons-categories",
        "hidden": ""
    },

So, I propose we put this information verbatim in a new metadata attribute for each image which will be populated with the get_imageinfo() request.

Image attribution and usage info are also in this property, so I'll re-open #104 to address it with the same approach.

[siznax]

Note: this image metadata is called extmetadata because it comes from Extension:CommonsMetadata which appears to be stable.

[siznax]

See also Commons:Assessments.