cubicweb-tracker #1433333 assignee relation for tickets [validation pending]

Would be nice to have this feature so we can make the relation between CWUser and Ticket to know who: will be/is/was working on a specific ticket.This way we could also have other features like my to-do list or my assignments, etc. That would very useful if a dashboard is set on the top of tracker for instance.

done in1.15.0
load left0.000
closed by#cbab3eb96b35 [schema/view] add assigned_to relation to Ticket (closes #1433333)
patch[schema/view] add assigned_to relation to Ticket (closes #1433333) [applied][view] update ProjectTicket view with todo_by relation (related to #1433333) [folded]