code: function composePage(pageData, locals) {
    const layoutReference = pageData.layout,
      pageDataNoConf = references.omitPageConfiguration(pageData);
  
    return components.get(layoutReference)
      .then(layoutData => mapLayoutToPageData(pageDataNoConf, layoutData))
      .then(fullData => resolveComponentReferences(fullData, locals));
  }
docs: Compose a page, recursively filling in all component references with
  instance data.
  @param  {object} pageData
  @param  {object} locals
  @return {Promise} - Resolves with composed page data