[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 their stage changed. A email template is sent 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.
[IMP] website_livechat : make it depend on rating_livechat. It now propose to display livechat channel on website pages, with its ratings and description.