Check for presence of user in other depts before deactivating

[adambray]

Deactivating a user in one department causes them to be deactivated for
all departments. I think we should fix it to make it
department-specific, since, for example, a user may opt to take a
semester off in one department but continue work in another.

Steven

---

Steven Le
IO Student Tech

[adambray]

This behavior is somewhat available already, in that you can always remove dept membership for a person.

However, we should generate a warning if you try to deactivate users who are members of a dept other than yours.