When editing a label with an group ID and u delete it, labelme crashed:
Fixed error "TypeError: setData() takes no keyword arguments"
Deleting the keywords fixed this error

Since pillow version 7 works on Windows, there is no need to specifically
install version 4 any more, so take this instruction out of the readme.

On Windows, the `source` command produces an error:

    'source' is not recognized as an internal or external command,
    operable program or batch file.

So update the setup instructions to invoke the `conda` binary instead.

* fix issue with grayscale images in draw_json

* Update draw_json.py
Co-authored-by: NKentaro Wada <www.kentaro.wada@gmail.com>

* Add support for png files

* Updates

Close https://github.com/wkentaro/labelme/issues/588