[MIGRATED] website_forum: migrated website_forum into new api + solved s...

...ome bugs

[IMP] website_forum: removed unnecessary imports
[IMP] website_forum: improved badges access for anonymous user
[IMP] wesite_forum: bug solved for ckeditor

- Task: https://www.odoo.com/web?&debug=#id=9031&view_type=form&model=project.task
- Pad: https://pad.odoo.com/p/r.4HSUoPQ9tBfdQEdN
In the _get_posts_count method read_group is not feasible because it use post_ids which is M2M field