#829 add new class to represent clinical assessments (handedness, tumor grading)

[Mathias]

During the OBI meeting in San Diego one of the topics coming up during reviewing assays was that we need a class to represent things like handedness assessment or tumor grading. Those are currently under assay (Definition: A planned process with the objective to produce information about the material entity that is the evaluant, by physically examining it or its proxies.). At the OBI meeting there was general agreement that those entities aren't assays. I suggest we create a superclass to assay At this point I want to start a discussion of how that class should be named, what its properties are and how to axiomatize it.