Make ensure_server async
Merge remote-tracking branch 'chiiph-github/bug/ensure_server_async' into develop
Force protobuf version to >=2.4.1.

* Also, generate events_pb2.py file using 2.4.1.
Add events for SMTP signaling.
Merge remote-tracking branch 'drebs/feature/3464_make-smtprelay-emit-signals' into develop
add new events for imap and keymanager
Merge remote-tracking branch 'kali/feature/imap_keymanager_events' into develop
Add libssl-dev requirement for pyOpenSSL.
Add IMAP_UNREAD_MAIL event
Merge remote-tracking branch 'ivan/bug/add-missing-dependency' into develop
Merge remote-tracking branch 'chiiph-github/feature/add_unread_imap_event' into develop
Update requirements

* Use requirements.pip
* Update reqs
Add versioneer to handle versioning here too.
Merge remote-tracking branch 'kali/bug/update_deps' into develop
Merge remote-tracking branch 'kali/feature/add_versioneer' into develop

Conflicts:
	setup.py
Fold in changes
Merge branch 'release-0.3.1'