[fix] website_forum : done fixes to make accept_answer toggle button fun...

...ction properly and made single answer selected at a time

 - Task: https://www.odoo.com/web#id=9064&view_type=form&model=project.task&action=333&active_id=131
 - Pad: https://pad.odoo.com/p/r.xrRcesVUGLE3v9Uo