This bug was caused by making it so that non-embossed modifier icon
buttons could become an operator button and retain their red highlight
for disabled modifiers. The icon button needs emboss turned off, but
in earlier versions of Blender, UI_EMBOSS_NONE would be overridden
by animation or red alert states.

Instead of abusing "NONE" to mean "none unless there is animation or
red alert", this commit adds a new emboss flag for that situation,
UI_EMBOSS_NONE_OR_STATUS, which uses no emboss unless there is an
animation state, or another status. There are only a few situations
where this is necessary, so the change isn't too big.