LPS-46460 Comments API: transfer all Message Boards references from BlogsEntryLocalServiceImpl

Hi @rotty3000!

This PR is for the **Blogs** subsystem. It's part 1 of 2 in removing MB references from the BlogsEntry local service. As soon as it gets in master, I'll follow with part 2: Spring wiring the CommentManager.

Please send back to me or forward to @sergiogonzalez at your discretion.

(Already has the contributions from @marcellustavares review.)