Added plot_image to __all__
Added plot_image to __all__

stiphyMT/plantcv,AntonSax/plantcv,danforthcenter/plantcv,jshoyer/plantcv,stiphyMT/plantcv,AntonSax/plantcv,danforthcenter/plantcv,stiphyMT/plantcv,jshoyer/plantcv,danforthcenter/plantcv