Embeddable CWL workflow rendering

## Description

The journal GigaScience has suggested a feature to be able to embed as an `` (or using JavaScript) a lightweight version of a workflow page.

This could be only the interactive diagram, only the input/output tables, or both - but skipping the usual headers and footers and having styling so it fits in an <iframe>.

One way would be to extend the current permalinks at the bottom to include `?format=html&embed=true` or even `embed=diagram`.

It could also be nice to have an "embed" pop-up with HTML snippet, like in YouTube, that shows a suggested `<iframe>` of a reasonable size. This might be version-bound by git commit or according to the current branch.