core: Nameplate sub-widgets should ignore alpha (#699)

It's a common practice to hide nameplates by adjusting their alpha,
but this has adverse effects on blizzard-managed widgets, affecting
gameplay in an (usually) accidental way.

ouf.lua

@@ -834,11 +834,13 @@ function oUF:SpawnNamePlates(namePrefix, nameplateCallback, nameplateCVars)
 			if(nameplate.UnitFrame) then
 				if(nameplate.UnitFrame.WidgetContainer) then
 					nameplate.UnitFrame.WidgetContainer:SetParent(nameplate.unitFrame)
+					nameplate.UnitFrame.WidgetContainer:SetIgnoreParentAlpha(true)
 					nameplate.unitFrame.WidgetContainer = nameplate.UnitFrame.WidgetContainer
 				end
 
 				if(nameplate.UnitFrame.SoftTargetFrame) then
 					nameplate.UnitFrame.SoftTargetFrame:SetParent(nameplate.unitFrame)
+					nameplate.UnitFrame.SoftTargetFrame:SetIgnoreParentAlpha(true)
 					nameplate.unitFrame.SoftTargetFrame = nameplate.UnitFrame.SoftTargetFrame
 				end
 			end