Display visible users only for when adding project members (#11724).

git-svn-id: http://svn.redmine.org/redmine@13586 e93f8b46-1217-0410-a6f0-8f06a7374b81
Don't load user activity for API responses (#18128).

git-svn-id: http://svn.redmine.org/redmine@13587 e93f8b46-1217-0410-a6f0-8f06a7374b81