Improve performance for Client combo

This avoids creating lots of extra python objects when
adding new clients. Instead of using ClientView which is expensive,
just query for Person.name and Client which is all we need in
these combos.

Should reduce the time to show clients from 5 seconds+ to 1.6 on
my machine.

Change-Id: I8f8b4545e466a7428fe4d06b9d941a3fcdf42083