[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
@rim-odoo : if one task or issue is reopened 3/4 times and each has rating means, first time customer get an email he is unhappy, the task/issue reopened again we send an email  he said ok and third time he said happy.
Now, for this particular task/issue we have 3 rating which should i consider or do we have to consider all means avg of all rating?