Handle alternative image_modes

[donaldgray]

Handle alternative image_modes - predominately CMYK. Outline of changes:

• in _uncompress_tiff check if the image_mode is a known type. If not:
  • Call _convert_img_colour_profile to change it to RGB and save
  • Write new file to stream + reload to get as PIL.TiffImagePlugin.TiffImageFile and access to tags
  • Check if XResolution and YResolution tags are present, if not set values from source image (unsure why these are being dropped).
  • Save to disk

Other changes:

• Add I;16B to known image_types. KDU handles these okay but Pillow only has limited support, conversion results in distorted image.
• When looking up dict for image type, call .lower() on suffix to handle, e.g. .TIF as .tif.
• Update base docker image and Pillow dependency