[ADD] added rating, rating_project and rating_project_issue module

 - Task : https://www.odoo.com/web#id=8060&view_type=form&model=project.task
 - Pad : https://pad.odoo.com/p/r.2BmKqyvcwKbiXPRI

[IMP] Added option to install rating module under Project

[IMP] added template to display when customer rates the task/issue

[IMP] Improved template and code

[IMP] : rating , rating_project and rating_project_issue as per new api

[IMP]: rating template

[FIX] : test case failed

[IMP] : code
percent_happy_issue : renamed in percentage_satisfaction_issue, and rename the compute function in _compute_percentage_satisfaction_issue

Then redifine the `_compute_percentage_satisfaction_project` with `api.depends('percentage_satisfaction_task', 'percentage_satisfaction_issue')`, and compute it with

@api.multi
    @api.depends('percent_happy_task', 'percent_happy_issue')
    def _compute_percentage_satisfaction_project(self):
        super(Project, self)._compute_percentage_satisfaction_project()
        Rating = self.env['rating.rating']
        for record in self:
            # get the number of rated tasks and issues
            nbr_rated_task = Rating.search_count([('res_model', '=', 'project.task'), ('res_id', 'in', record.tasks.ids)])
            nbr_rated_issue = Rating.search_count([('res_model', '=', 'project.issue'), ('res_id', 'in', record.issue_ids.ids)])
            nbr_project_rating = nbr_rated_issue + nbr_rated_task
            # compute the weighted arithmetic average
            ratio_task = float(nbr_rated_task) / float(nbr_project_rating) if nbr_project_rating else 0
            ratio_issue = float(nbr_rated_issue) / float(nbr_project_rating) if nbr_project_rating else 0
            record.happy_customer = round((ratio_task*record.happy_customer)+(ratio_issue*record.percent_happy_issue))