Allow defplan functions to use action return values as simlple clojure values

When writing plan functions, action return values can not be directly accessed, as they are not available until execution time.  Pallet has facilities (`delayed`, `plan-when`, etc) for handling these values, but this imposes a cognitive load on the developer.

This pull request allows plan functions to be written without the pallet specifc code, and it will be transformed into code that uses the correct pallet forms.