Add image license info

[matkoniecz]

to use image correctly one needs to know about its license - for example what, if any, attribution is required

from looking at https://github.com/siznax/wptools/wiki/Images this library has no function with such functionality

[siznax]

Hi @matkoniecz. Mediawiki API:Imageinfo does not offer license information. It is the user's responsibility to make proper use of API data as described in API: Licensing.

[siznax]

As mentioned in #105, it turns out that API:Imageinfo does offer image license info with iiprop=extmetadata, e.g.

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": {
    "Credit": {
        "value": "Self-published work by <a href=\"//commons.wikimedia.org/wiki/User:Dschwen\" title=\"User:Dschwen\">Dschwen</a>",
        "source": "commons-desc-page",
        "hidden": ""
    },
    "Artist": {
        "value": "<a href=\"//commons.wikimedia.org/wiki/User:Dschwen\" title=\"User:Dschwen\">Dschwen</a>",
        "source": "commons-desc-page"
    },
    "LicenseShortName": {
        "value": "CC BY 2.5",
        "source": "commons-desc-page",
        "hidden": ""
    },
    "UsageTerms": {
        "value": "Creative Commons Attribution 2.5",
        "source": "commons-desc-page",
        "hidden": ""
    },
    "AttributionRequired": {
        "value": "true",
        "source": "commons-desc-page",
        "hidden": ""
    },
    "LicenseUrl": {
        "value": "http://creativecommons.org/licenses/by/2.5",
        "source": "commons-desc-page",
        "hidden": ""
    },
    "Copyrighted": {
        "value": "True",
        "source": "commons-desc-page",
        "hidden": ""
    },
    "Restrictions": {
        "value": "",
        "source": "commons-desc-page",
        "hidden": ""
    },
    "License": {
        "value": "cc-by-2.5",
        "source": "commons-templates",
        "hidden": ""
    }

So, we'll put all of this info, verbatim, into a new metadata attribute for each image.

[lisongx]

@siznax
thanks! This is really useful!

[siznax]

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

[siznax]

Including this in the next release. Thanks so much for opening this issue @matkoniecz!