Accept POST on supported REST collections

POST on /groups/ should create a new resource whose id is
determined from the input body. The AcceptsCreate interface
does not work here as there was no id in the path remaining.
Build a new interface AcceptsPost that handles POST calls on
a collection using the collection itself to construct the view.
This is primarily meant for TopLevelResource collections.

Change-Id: I0086ffc69cf42905db8c98198a809bfa755b52dd
2 files changed