models: change edit permissions for comments

models: change edit permissions for comments

Change patch comments' edit permissions to match that of the patch
associated with the comment (i.e. patch author, project maintainers, and
delegate) and add permissions for both patch and cover comment authors
to be able to change the `addressed` status of comments as well. For
cover comments, add permissions to edit for cover submitter and project
maintainers.

Signed-off-by: Raxel Gutierrez <raxel@google.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>