Krishna to issue 363

[pbuttigieg]

Closes #1261

[pbuttigieg]

Content review:

Both of these are dubiously placed under PATO:electromagnetic (EM) radiation quality defined as:

A physical quality that inheres in an bearer by virtue of how that bearer interacts with electromagnetic radiation.

Is the flux or its density interacting with EM radiation?

The subclass axioms were built as if they're equivalence axioms. These will be changed substantially.

• photosynthetic photon flux - now a flux.
• photosynthetic photon flux density - This can't be put under PATO:mass density as photons don't have mass in the regular sense. The definition reads more like a rate of receiving quanta of PAR on a surface. Thus represented this as a rate associated with a new class for irradiation of a surface with PAR. This is likely to need domain expert + ontologist revision in the future.

I created a stub hierarchy for irradiation, which should be expanded if it holds.