Fig compatibility layer 649

TODO deal with port edge cases, e.g. just container port specified, or IP and port specified on host
See http://www.fig.sh/yml.html
Issues have been raised for this missing functionality, which is not yet supported by Flocker.

Fixes #649
`from __future__ import unicode_literals` negates the need to prepend `u` to string literals,doesn't it? Should I still explicitly declare the literals as `unicode` anyway?