Switch vumi.config to confmodel.
Compat import of IConfigData in vumi.config.
Remove trailing comma.
Use new confmodel fallback fields.
Set .required_fields instead of overriding .present().
Merge branch 'develop' into feature/issue-806-switch-to-confmodel
Update to confmodel-0.2.0 with new module layout.
Merge branch 'feature/issue-806-switch-to-confmodel' into develop