feat(Listing Admin): Add basic REST call to get all by parameters
feat(Listing Admin): Listing counts
feat(Listing Admin): Adding query params to HAL URIs
feat(Listing Admin): Fix count when using approvalStatus parameter
test(PagedResultList): Creating testutil for mocking PagedResultList
test(Listing Admin): OZF-561 ListingResource test
feat(Listing Admin): OZF-464 Parameterized Listing Admin REST call

The /api/listing REST call has been changed in both purpose and use.
While it was previously meant to give any user access to the general
list of listings, it has now been locked down to only admins and org
stewards.  General users can still browse listings via the search
calls.  The new /api/listing now accepts the following URI query
parameters, in addition to the paging parameters that it used to
support:

* `org` The title of the organization to get listings for
* `approvalStatus` The approvalStatus enum constant to get listings for
* `enabled` The enabled/disabled status to get listings for

Each of these parameters acts as an optional filter on the listings
returned.  Note that when the current user is an org steward, the
`org` parameter must be one of the organizations that they are a
steward of.  If an org steward does not specify an `org` to filter by,
the listings will be filtered to those in any organization that the
user is a steward of.

In addition to the new parameters, the call has additions to its
response.  It now has a top-level "counts" object in the json which
contains the total number of listings matching the query parameters for
each of the following categories: enabled, each approvalStatus, and
each organization in the system.

Breaking changes:  The /api/listing REST endpoint is no longer
accessible for non-steward users.