cubicweb #343596 make sure content-negociation works [open]

when one sends an HTTP request with "Accept: application/rdf", make sure cw returns the 'rdf' view and when the content-type is text/html, make sure cw returns the 'html' view.

to be more general, provide a map of content-type -> vid. this will lead to better REST support.

prioritynormal
typeenhancement
done in<not specified>
load0.500
load left0.500
closed by<not specified>