Render "document" properties with full content in Page Model API

In Authentic's flavor of dynamic components, they use a naming convention to treat any property ending in the literal string "document" as if it contains a JCR path to a document. Their component implementations will lookup any document at that path and render its content in the Page Model API output. We should investigate whether we want to implement a similar feature, or use some more explicit mechanism that would be a closer equivalent to a @JcrPath annotation for the parameter.