[Add] Cache models on instantiation

...to remove need for Edit to persist these immediately, which in
turn causes #770 and #678

platform/core/src/services/Instantiate.js

@@ -44,10 +44,15 @@ define(
          * @param {IdentifierService} identifierService service to generate
          *        new identifiers
          */
-        function Instantiate(capabilityService, identifierService) {
+        function Instantiate(
+            capabilityService,
+            identifierService,
+            cacheService
+        ) {
             return function (model, id) {
                 var capabilities = capabilityService.getCapabilities(model);
                 id = id || identifierService.generate();
+                cacheService.put(id, model);
                 return new DomainObjectImpl(id, model, capabilities);
             };
         }