Ability to install with opencv-headless, remove altair dependency etc.

[ogencoglu]

Currently plantcv requires opencv-python which comes with a lot of bloat (GUI, libGL etc) if those are not needed. Typical solution for projects that do not need that is simply using opencv-python-headless. Similarly altair and such visualization libraries are not needed for core functionalities.

It would make sense to have a separate, distilled plantcv that does not require especially full opencv install. In addition, library versions in plantcv are not fixed and might change the behaviour. I suggest those to be fixed as well in pyproject.toml.