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

Hi @rotty3000!

This PR is for the **Blogs** subsystem. It's the one we were working on together today: [this](https://github.com/rotty3000/liferay-portal/pull/466), plus [all your changes](https://github.com/arboliveira/liferay-portal/pull/14) to wire the CommentsManager via Spring and RegistryUtil, plus my final touches on the unit tests.

The [last commit of all](https://github.com/arboliveira/liferay-portal/commit/c9779699e36814e0f152c3ff2758ba15ba2fffc7) is the one you mentioned will probably get in master through a different pull request. I moved it to the end so you can easily drop it in case of rebase conflict.

Thanks!!