Create EntityResponse class that REST methods can return

## Create EntityResponse class that REST methods can return

Issue #55 allows any ArraySerializableInterface to be returned from a rest method.  This makes testing easier, but the problem it meant to solve still exists if the response code is something other than 200, in which case a Response object must be returned, which contains only an array copy and not the entity itself.  Creating a DataObject class called EntityResponse that contains both the status code and an ArraySerializableInterface will solve this problem.