add PASCAL VOC labels

Some segmentation models are trained on PASCAL VOC, so it's useful to have those labels in the repo.

pascal-voc-id2label.json

@@ -0,0 +1 @@
+{ 0: "background", 1: "aeroplane", 2: "bicycle", 3: "bird", 4: "boat", 5: "bottle", 6: "bus", 7: "car", 8: "cat", 9: "chair", 10: "cow", 11: "diningtable", 12: "dog", 13: "horse", 14: "motorbike", 15: "person", 16: "pottedplant", 17: "sheep", 18: "sofa", 19: "train", 20: "tvmonitor" }