Settings screens redirect for certain roles

Closes #3291
- Adds redirects based on roles as defined in the case
- Adds new mixin `CurrentUserSettings`
- For authors, all settings pages redirect to `users/self`
- For editors, all settings pages other than specific users redirect to `users`. Any user that is not self or an author redirects to `users`
Merge pull request #3416 from alarobric/case_3291

Settings screens redirect for certain roles
User API ability to filter users by role

refs #3446

- This only covers the API changes needed for #3446
Merge pull request #3455 from ErisDS/issue-3446

User API ability to filter users by role