Add a UsagesResource.getUsageStatus API endpoint

[csjx]

After discussion, we realized that we need a non-authenticated API endpoint that allows public users to find out whether a given portal's usage (by its instanceId and quotaType) is active. This allows us to conditionally render paid features for the portal.

• [x] Add the GET /usages/status?instanceId=:instanceId&quotaType=:quotaType method to the Swagger API
• [x] Create a UsageStatus model with one status property with values of active or inactive:

  {
  "status": ":status"
  }

  Note: Should the UsageStatus model also include the "object": "usagestatus" field to be consistent with our other models?

• [x] Modify UsagesResource and add the getStatus() method (leave out the @PermitAll annotation) which returns a UsageStatus model in 200 responses, otherwise 404 if not found.
• [x] Write up a UsageTest serialization/deserialization unit test for the model using a usagestatus.json fixture

[gothub]

Added in these commits:

• a9f20c1daa857521a58bedcc908f2c57239a6ebf
• 5ba6aa7814ac12925daf0e2b9bce689dab306eb4
• a488674a4a489219b754c1c874b7d29e8d6de3b8
• 50a8dabf7f0980562b56ce58d7cc32a478edaf17