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
I would suggest leaving the fig detection method on this class, and then you can do if/else instead of try/except. That way the parser can just assume it's fig format.