Filter private usernames in selectize functions

[cycomachead]

Checklist

• [ ] I have read the Contribution & Best practices Guide.
• [ ] My branch is up-to-date with the upstream master branch.
• [ ] The tests pass locally with my changes.
• [ ] I have added tests that prove my fix is effective or that my feature works(if appropriate).
• [ ] I have added necessary documentation (if appropriate).

Short description of what this resolves/which issues does this fix?:

-

Changes proposed in this pull request:

-