search through admins, credentialed and inactive if selected as a field source

[i-just]

Description

v5 version of PR 1337. It has the same approach to handling groups and admins, and adds handling of credentialed and inactive sources.

Related issues

844

[angrybrad]

@i-just hopefully I resolved the merge conflicts for the v4 and v5 version of this correctly!

[i-just]

Thanks, @angrybrad 🙂 I had a look through and gave it a quick test, and looks fine in v4 and v5.