Add back six dependency and change pbtxt files to reflect new way of using own...

Add back six dependency and change pbtxt files to reflect new way of using own data to train object recognition models

object_detection/data/pascal_label_map.pbtxt

-item {
-  id: 0
-  name: 'none_of_the_above'
-}
-
 item {
   id: 1
   name: 'aeroplane'

object_detection/data/pet_label_map.pbtxt

-item {
-  id: 0
-  name: 'none_of_the_above'
-}
-
 item {
   id: 1
   name: 'Abyssinian'

object_detection/utils/visualization_utils.py

@@ -26,6 +26,7 @@ import PIL.ImageColor as ImageColor
 import PIL.ImageDraw as ImageDraw
 import PIL.ImageFont as ImageFont
 import tensorflow as tf
+import six
 
 
 _TITLE_LEFT_MARGIN = 10