Authors restricted to authorized users in current project

[fboes]

This plugin lists all users of Redmine to be selected as new authors. This results in the select field being rather long in big Redmine installations. It is also possible to assign an author who has no access rights to the current project.

A possible solution is to be only able to select users who have at least some kind of rights in the given project. The functionality could mirror the functionality of the "Assigned to" field.