Work out a neat way to ref nested resources in templates

[jamesroutley]

Currently, we can ref AtomicTemplates with ref(atomic_template.name). If we want to ref a resource which is contained within another template, we must ref it's actual name. This is unsafe as resource names may change on compilation if they clash with another resource name.

• Could be done by storing merged templates in a collections.OrderedDict rather than a list. Users could then access the nested resource with template.templates[<atomic_template>.name]. This could get verbose with multiple nested templates.