[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
if i use type="float" , it will break , ParseError: "'Selection' object has no attribute '_setup_digits'" while parsing /home/bak/runbot/extra/runbot/static/build/28675-master-rating-dja-ee347c/openerp/addons/account/data/account_data.xml:44

Because of `def clear_cache(self, cr)` method in decimal_precision module: