Config option to use the filenames as key in the metadata

[wutzebaer]

Currently the metadata can only mapped my the basename. It would be nice to have the option to use the full filename.

{
    "0.png": {
        "name": "dsfsdf",
        "description": "The best shapes around",
        "image": "No URL/0",
        "attributes": [{
                "trait_type": "Background",
                "value": "Purple Background"
            }, {
                "trait_type": "Body",
                "value": "Main Body"
            }, {
                "trait_type": "Hat",
                "value": "Triangle Hat"
            }, {
                "trait_type": "Weapon",
                "value": "none"
            }
        ]
    }
}