Interpret the power property of light correctly.

[JiayinCao]

Current implementation is not energy consistent. The task is to make it consistent, meaning that for example, even if the size of area light changes, its total power doesn't change.

After this task, SORT will generate consistent light energy result with cycles.

[scorpius]

I always have to multiply my area lights by 3, which is kind of odd. But it might be because the lights are scaled and the plugin doesn't take that into account. This render is with the latest git version, but uses OIDN along with low samples.

It's not a big deal but I'll have to do more tests...