[ITree] small fixes: parent_entity is a IBreadCrumbs method, we should use .parent on ITree

restore bw compat on Entity.related_rql

reledit refactoring * js handling rewritten to exploit all form capabilities (such as file upload ...) * attribute-like composite relations (one ttype, cardinality in '?1' from composite side) are more cutely handled, with a 'add'/'delete' additional actions/icons * a reledit_ctrl rtag to finely control: reloading, edition and default values * a proper chapter in the documentation (book) * many bugfixes