ADE20k's label names are not appropriate

[Sosuke Kobayashi]

For example, the list ade20k_semantic_segmentation_label_names has two "tree"
https://github.com/chainer/chainercv/blob/master/chainercv/datasets/ade20k/ade20k_utils.py#L27
https://github.com/chainer/chainercv/blob/master/chainercv/datasets/ade20k/ade20k_utils.py#L95

Some values are different from the original in https://github.com/CSAILVision/sceneparsing.

[Sosuke Kobayashi]

https://github.com/CSAILVision/sceneparsing/blob/master/objectInfo150.txt
The current values may be extracted from the last column of this file, followed by splitting it with a blank and picking the last element. So, class palm, palm tree is converted to tree.

[Yusuke Niitani]

I remember extracting label names from that text file. (also in csv format https://github.com/CSAILVision/semantic-segmentation-pytorch/blob/master/data/object150_info.csv)
I should have been more carefully with parsing names.