fix circular dependency issues relating to request models

src/app/core/data/rest-request-with-response-parser.model.ts

@@ -0,0 +1,14 @@
+import { RestRequest } from './rest-request.model';
+import { GenericConstructor } from '../shared/generic-constructor';
+import { ResponseParsingService } from './parsing.service';
+
+/**
+ * A RestRequest with a method to retrieve the ResponseParsingService needed for its response
+ */
+export abstract class RestRequestWithResponseParser extends RestRequest {
+
+  /**
+   * Get the ResponseParsingService needed to parse the response to this request
+   */
+  abstract getResponseParser(): GenericConstructor<ResponseParsingService>;
+}