nack for cellulant USSD
adding nack for httprpc
adding nack to infobip
adding nack to integrat
adding nack for mediaedgegsm
adding nack to mediafonemc
adding nack to mtech_ussd
adding nack for safaricom
adding nack to smssync
adding nack to twitter
adding nack to vas2nets
adding nack to vodacom_messaging
Merge branch 'develop' into feature/issue-399-add-nack-to-all-transports
using defer.succeed & defer.fail (thanks @jerith)
use single quotes (thanks @jerith)
returning more explicit nack reasons (thanks @jerith)
Merge branch 'feature/issue-399-add-nack-to-all-transports' into develop
missing commit from the nack PR (thanks @jerith)
Merge branch 'develop' into feature/issue-457-endpoints-and-connectors

Conflicts:
	vumi/transports/integrat/tests/test_integrat.py