Serialize ACSet presentations to JSON with JSON Schema validation

[aaguinal]

Add the ability to serialize and deserialize ACSet presentations, such as SchWeightedGraph, SchGraph, etc. using a JSON format similar to the one shown below:

{
    "version": {
        "ACSetSchema": "0.0.1",
        "Catlab":  "0.13.0"
    },
    "Ob": [
        {
            "name": "V"
        },
        {
            "name": "E"
        }
    ],
    "Hom": [
        {
            "name": "src",
            "domain": "E",
            "codomain": "V"
        },
        {
            "name": "tgt",
            "domain": "E",
            "codomain": "V"
        }
    ],
    "Attr": [
        {
            "name": "weight",
            "domain": "E",
            "codomain": "Weight"
        }
    ],
    "AttrType": [
        {
            "name": "Weight"
        }
    ]
}