Fix/comments permissions

https://www.openproject.org/work_packages/14430
@hschink, @manwithtwowatches, now you got me totally confused. I would say the following:
* If the user is the creator of the note and he has the edit_own_work_package_notes permission, he is allowed.
* If the user is not the creator of the note and he has the edit_own_work_package_notes permission, he is not allowed.
* If the user has the edit_work_package_notes permission, he is allowed regardless of the authorship.

Where do we disagree? I am asking because the code says we do.