support empty names in auto slug generation

http://manage.dimagi.com/default.asp?141834
Merge pull request #4537 from dimagi/empty-codes

support empty names in auto slug generation
update staging.yaml

[ci skip]
Merge remote-tracking branch 'origin/jsonobject-0.6.0b2' into autostaging
Merge remote-tracking branch 'origin/explicit_case_processing' into autostaging
Merge remote-tracking branch 'origin/master+schedule+schedule' into autostaging
Merge remote-tracking branch 'origin/hq-dropdown' into autostaging
Merge remote-tracking branch 'origin/logos+master' into autostaging
Merge remote-tracking branch 'origin/archive-programs+custom_product_data' into autostaging
Merge remote-tracking branch 'origin/subscription-no-contact-info' into autostaging
Merge remote-tracking branch 'origin/revert-4205-revert-3841-86347-2' into autostaging
Merge remote-tracking branch 'origin/bulk-app-translate' into autostaging
Merge branch 'callcenter' into autostaging
Merge remote-tracking branch 'origin/reduce-location_' into autostaging
Merge remote-tracking branch 'origin/help-text' into autostaging
Merge remote-tracking branch 'origin/masterlist-workflow' into autostaging
Merge remote-tracking branch 'origin/domain-metadata' into autostaging
update submodule refs