New rangebreaks and unified hover should work from templates

I should be able to set `rangebreaks` and `hovermode="x unified"` inside `layout.template.layout` instead of `layout` and have things work identically.

As an aside: this is an invariant which should be the case for all attributes! I just QA'ed these two by chance but we should probably look into previous recently-added attributes to ensure that they work.