Enhancement: Automatic token effects based on attribute/property changes

[sPOiDar]

I've been thinking for a while about adding a shadow when a token's height field is updated, that increases its diffuse the higher the height goes.

Now, with splash, we might add a momentary effect when a token's HP goes down, and possibly some effect when HP goes up.

Noting here so I don't forget, I'll take a look at it when I find some time.