adding twisted endpoint option for SMPP transport
test for when using endpoints
updated docstring for why we still need host & port in the config
Merge branch 'develop' into feature/issue-491-smpp-endpoints
Merge branch 'develop' into feature/issue-491-smpp-endpoints

Conflicts:
	vumi/transports/smpp/clientserver/config.py
	vumi/transports/smpp/transport.py
returning endpoint strings instead of objects
endpoints for smpp
Revert "returning endpoint strings instead of objects"

This reverts commit 2e7b0660dd347756c1e2d259449b5dec0c05184a.
smpp w/ endpoints
unused import
Merge branch 'feature/issue-491-smpp-endpoints' into develop