1.2.1 Children and parents export

The entity number of the parents and the child of each entities are now exported as well

{
    "entity_number": 13,
    "name": "transport-belt",
    "position": {
        "x": 0.5,
        "y": -90.5
    },
    "usage_rate": 0.084,
    "transpoted_items": {
        "iron-plate": 1.26
    },
    "parents": [
        11
    ],
    "children": [
        12,
        14
    ]
},