[FIX] Kanban / Modal - Close the backdrop from dialog when we open the dialog...

[FIX] Kanban / Modal - Close the backdrop from dialog when we open the dialog for add a new column in kanban view. This bug was introduced since with use bootstrap modal

bzr revid: jke@openerp.com-20140509131203-4gy3nhlj0v6fk7zv