Add a card loader that can load JSON files

[skiwi2]

A card loader should be added that can load JSON files, example file format:

{
    "cardinfo": {
        "cards:" [
            //cards here
        ]
    }
}

[skiwi2]

Updated the JSON file format to use a "cardinfo" root element, such that other properties can be added if necessary.

[Phrancis]

Closing as duplicate. See #183 and #190 for reference