Nested layouts: moved templates to make testing more effective

It's easier to quickly find errors if you're using all of the available templates. What I found after moving the layouts and pages from ./nested/ into the dirs with the other layouts and pages is a couple things:

* all partials throw an error, regardless of whether they are in a layout or a page
* the layouts aren't inheriting. meaning that only the "last" layout is actually used. 

I'll make another pull request with more complicated nesting if I get a chance, but this made me realize that we should be testing more complicated scenarios in general in this repo. There aren't very many partials here, and the ones that are here are very basic. Anyway, hope this helps track down whatever the error is.