scifight/admin.py: customize empty label for identity combo-boxes
scifight/admin.py: customize empty label for identity combo-boxes

Signed-off-by: Pavel Kretov <7cae407f1f3b56350827d1394be40a3e8f9cb303@gmail.com>

turboj55/scifight,scifight/scifight,turboj55/scifight,scifight/scifight,scifight/scifight,turboj55/scifight