Enable workflow display_by_username_and_slug to support different 'display' formats: html, json, and json download. This makes it possible to generate human-readable URLs for all workflow display/download/export actions. Update download and export links to use display_by_username_and_slug.
Fix 07508592cb65 bug to correctly set username for workflow download/link.
Add save and link options for embedded workflows.
To ensure that workflow has a slug, create slug when retrieving workflow from database. Remove slug creation code from user controller actions.