yolovx support added

[vtpl1]

Support yolox models.
Solves #406

sample model_proc file

{
    "json_schema_version": "2.2.0",
    "input_preproc": [],
    "output_postproc": [
        {
            "converter": "yolo_vx",
            "iou_threshold": 0.4,
            "classes": 80,
            "labels": [
                "person",
                "bicycle",
                "car",
                "motorbike",
                "aeroplane",
                "bus",
                "train",
                "truck",
                "boat",
                "traffic light",
                "fire hydrant",
                "stop sign",
                "parking meter",
                "bench",
                "bird",
                "cat",
                "dog",
                "horse",
                "sheep",
                "cow",
                "elephant",
                "bear",
                "zebra",
                "giraffe",
                "backpack",
                "umbrella",
                "handbag",
                "tie",
                "suitcase",
                "frisbee",
                "skis",
                "snowboard",
                "sports ball",
                "kite",
                "baseball bat",
                "baseball glove",
                "skateboard",
                "surfboard",
                "tennis racket",
                "bottle",
                "wine glass",
                "cup",
                "fork",
                "knife",
                "spoon",
                "bowl",
                "banana",
                "apple",
                "sandwich",
                "orange",
                "broccoli",
                "carrot",
                "hot dog",
                "pizza",
                "donut",
                "cake",
                "chair",
                "sofa",
                "pottedplant",
                "bed",
                "diningtable",
                "toilet",
                "tvmonitor",
                "laptop",
                "mouse",
                "remote",
                "keyboard",
                "cell phone",
                "microwave",
                "oven",
                "toaster",
                "sink",
                "refrigerator",
                "book",
                "clock",
                "vase",
                "scissors",
                "teddy bear",
                "hair drier",
                "toothbrush"
            ]
        }
    ]
}