Issue-93 Add subscription when creating check (partial REST API only)

POST to /checks API now supports persisting nested subsciption objects.
New acceptance test.
This patch does NOT address the UX changes necessary to create
subscriptions concurrently with checks, but is more narrowly focused at
supporting scripts.  It will generalize once someone is able to properly
factor the partials out in the angular.
Merge pull request #181 from DevinDawson/issue-93

Issue-93 Add subscription when creating check (partial REST API only)