Finish API documentation for the collection related endpoints
Report the error message
Improve API documentation for the API endpoint related to packages

Also make sure all the message are reported to the user when several action
are processed in one call.
Small text fixes in the messages/errors returned to the user
Replace owner by poc on the fedmsg messages as well
More text fixes on the message/error returned to the user
Fix the unit-tests for the changes made to the API and messages returned
Update the API documentation for the API endpoint related to packagers
Adjust unit-tests for changes made in the packagers API
Small change of wording as we no longer use the 'owner' word
Update API documentation for the API endpoints related to ACLs management