made optional data format args actually optional

[TTF2050]

Functions like add_image and add_video indicate that the dataformats arg is optional. However, there was no code to handle the None case. This commit adds a function that enables automatic determination of which channel is the color channel and invokes it whenever dataformats is None. It makes assumptions about the ordering of the other channels, but it should cover 80% of use cases.

[lanpa]

Closing as test is not passed after fixing trivial linting errors.