Don't chain imports with *
Don't chain imports with *

`logging` and the django `User` model were both being imported from
`users/signals.py`, hopefully by accident.  This adds those explicitly
as dependencies, and gets rid of the `import *`.

qedsoftware/commcare-hq,qedsoftware/commcare-hq,qedsoftware/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq