added permission to block message on hidden switches

[ChrissW-R1]

Closes #1298

[me4502]

If Spigot has broken empty messages not showing up, it makes sense to either fix that in Spigot or work around it in CraftBook, rather than adding another permission node. This doesn't really make sense to add, because who's to say someone else won't have a use case to hide a different message. It'd be much better to fix/work around the Spigot bug, not add a permission node for only a single message