Rename "Templates" to "Layouts"

As per the blog post & screencast, I had the issue of not really knowing what to call these "copies" of theme settings to be used contextually.

Per one of the comments on my blog post, the simple name of "Layouts" was suggested, as I DID actually use that term several times during the screencast.

I will be working in the interface to replace all instances and descriptions of "template" to "Layout".