Full support for blackout_restriction

Until now, blackout_restriction has been dummy data on
the Atlas API. With these changes, blackout restrictions
are properly supported in both GET and POST requests.

A new publisher has been added to support POSTing of
sparse content, which will be matched to existing
datasets to allow clients to provide blackout data.
Merge pull request #230 from atlasapi/mbst-9928-blackout-flag

Full support for blackout_restriction