Fixes #1596 by ensuring it only shows active members.

Currently removing a user from a group/org (marking membership as deleted)
then it still gets returned in dataset/new as a viable organisation/group to
choose when it isn't (as the user is not actually still a member).
Merge branch 'master' into 1596-dont-show-deleted-members
Merge branch '1596-dont-show-deleted-members'