Comment 12 for bug 1884950

Here's a branch:

https://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/user/berick/lp1884950-org-admin-scroll

* 1st commit makes the org unit tree scrollable.

* 2nd commit fixes an issue with the org unit service I found while testing. It now loads all org unit types, even if a given type has no org units linked. Without this, the org unit admin UI cannot add org units to an empty type.