280: Automatic Lights requires Custom Distance which requires EEVEE

[tngreene]

I picked Custom Distance and didn't realize that Cycles doesn't use that. In 2.80 EEVEE is the default, in 2.81 it is Cycles, and in 2.82 it appears they went back. Regardless of the default, people still have to be warned

-if they're in Cycles and they're in Lights Properties Tab and the light is a Spot and the light name has a size parameter

that they can't change the SIZE

And now here's the tough decision:

Should we give people an error for using the "wrong" rendering engine? Do we just use whatever setting the put in as long as they did it once?

My intuition says "don't have hidden UI silently work or fail", but, if people tell me they like switching in and out of EEVEE......... I still don't like it. We don't have an official rendering engine for XPlane2Blender but maybe if we one day get to material nodes we'll have to make a choice.

For now I think it'll be warning label and an error to stop people from being lost? We can always remove it and be more flexible later.

[tngreene]

This was solved by re-using Custom Light's size for size. See #568