[IMP]added subtype in blog to send notification of blog follower and add...

... follower in post when they comment on post.

Update website_blog.blog_post.js

Update test_ui.py

- Task: https://www.odoo.com/web#id=10039&view_type=form&model=project.task&action=333&active_id=131
- Pad: https://pad.odoo.com/p/r.cQKOHzo37oZPaAZS
And also check that blog followers have received the message.