cubicweb #1291286 easy way to link to existing or new entity [open]

as a user, I want to be able to easily link an entity to another existing entity or to a new one.

Example case, I'm using the book cube to manage a library. I want to set the author of a book.

Case 1: I know the author is not in the db, I use a link in the relation edition form to create a new Person

Case 2: I'm not sure if the author exists, so I browse for a Person, and after I have not found the Person, use a link in the interface to create a new Person.

In both cases, the creation form for the person is pre seeded with the author_of link to the Book.

UPDATE(nico): use a modal window where you can also paste a url (see comment below).

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