[ADD] rating : base rating module contains a mixin and the meta model rating with graph and kanban views
[ADD] rating_project, rating_project_issue : using the rating mixin, tasks and issues are rated when they changed stage. A email template is send to the customer of the object.
[ADD] rating_livechat, im_livechat : move the rating from im_livechat to rating_livechat. Now the customer feedbacks use the mixin.