Add logic for observations on parts of organisms

[ramonawalls]

This is an issue for the PPO (but unfortunately not on github), which needs to make inferences about the presence or absence of structures on a whole plant based on an observation of a plant part, either from a herbarium specimen or from an image of a plant part. However, I think the logic is needed more broadly and should be included in BCO.

PPO has addressed this issue by creating a class called "portion of plant", which is a proper part of a plant or "derived" from a proper part of a plant (the actual relations are not yet specified, because they don't exist in RO yet). PPO logic infers that is a structure is present on a part of a plant, it must have been present on the whole plant. If a structure is absent from the plant part, you cannot make an inference about its presence on the whole plant.

I suggest that BCO create upper terms with a similar design pattern that could be used in PPO or for other organisms.