[Persistence] Add in-line documentation

Add clarifying comments to reflect changes to
procedure used for loading models from persistence
introduced in support of reducing latency in loading
domain objects introduced by the WARP Server adapter,
WTD-644.

platform/core/src/models/PersistedModelProvider.js

@@ -22,10 +22,14 @@ define(
         function PersistedModelProvider(persistenceService, $q, SPACE) {
             function promiseModels(ids) {
                 return $q.all(ids.filter(function (id) {
+                    // Filter out "namespaced" identifiers; these are
+                    // not expected to be found in database. See WTD-659.
                     return id.indexOf(":") === -1;
                 }).map(function (id) {
+                    // Read remaining objects from persistence
                     return persistenceService.readObject(SPACE, id);
                 })).then(function (models) {
+                    // Packaged the result as id->object
                     var result = {};
                     ids.forEach(function (id, index) {
                         result[id] = models[index];