Run Bitmask in a docker container.
This is useful for:
- developers dogfood email in a separate environment allowing them to keep developing Bitmask and opening/closing the client
- as a starting point for a battery of tests for bitmask that will autologin, and check for arriving mails
(from redmine: created on 2015-09-04, closed on 2015-09-08, relates #7427 (closed), relates #6715 (closed))