refactor login box & form to enable easy pluggability
* vregistry.selectable: get all selectable object of fixed oid with given context
* template headeri, logbox, logform: reorganize a bit the structure
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html