#1370 Add a yellow warning for nested templates w/multiple sub-templates

[Ahasuerus]

Add a yellow warning for nested templates w/multiple sub-templates. The way the software currently works, you can only nest a single template inside of another template. Something like:

{{Narrator|{{A|Simon Jones (actor)}}, {{A|Christopher Cerf}}, {{A|Richard Dawkins}} and {{A|Stephen Fry}}}}

doesn't work correctly.