Fix bug preventing some template fragments from being included.
Fix bug preventing some template fragments from being included.

The nesting of the *_include blocks is unnecessary, and in at least one
theme (Dark Rainbow), caused template fragments to be ignored completely.

This change will be much easier on theme creators, since they won't have to
call {{ block.super() }} manually each time they override one of the common
blocks (e.g. stylesheets).

tylerbutler/engineer,tylerbutler/engineer,tylerbutler/engineer