Support Namespacing Layout vs Component Templates

[jonwinton]

With layouts being a top level data structure, we need to namespace layout/component templates. This means some helpers will need to reference the namespace + component name rather than just the component name.

For example: https://github.com/clay/handlebars/blob/master/partials/component-list.hbs#L2

[nelsonpecora]

Namespacing layouts would also require changes to kiln and claycli