cubicweb-card #1382558 Add a rql ReST directive [deprecated]

I think it might be handy to have a rql ReST directive available to insert dynamic content in a card. The standard eid directive is a bit too restrictive to me. I'd like to be specify any possible rql and specify a vid. Of course, only read-queries would be allowed.

It could even become a standard CubicWeb directive.