cubicweb-file #1341950 Use filename in the download url. [validation pending]

The current download url (file/<eid>?vid=downloadurl) is very annonymous. I think download url should be suffixed with the filename to help indexation, url sharing and automatic download.

appeared in<not specified>
done in1.12.0
load left0.000
closed by#a4f3a73499ae suffix download url by the filename. (closes #1341950)