Import voice transport from Vumi.
Merge branch 'feature/issue-1-add-setup-py' into feature/issue-2-import-freeswitch-transport-from-vumi
Fix import of voice transport in tests.
Merge branch 'develop' into feature/issue-2-import-freeswitch-transport-from-vumi
Use += instead of repeating self.current_input.
Remove unnecessary inlineCallbacks.
Merge branch 'feature/issue-2-import-freeswitch-transport-from-vumi' into develop