[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
this is not SQL (see runbot log). Try somthing like 
_sql_constraints = [
          ('check_rating_range_value', 'CHECK( CAST(rating as INTEGER) IN (-1,0,1,2,3,4,5,6,7,8,9,10))', 'The rating value must be between -1 and 10.')
    ]