Adds ability to reset data object

This commit can be dropped after this PR is merged:

#1952

data/service/data-service.js

@@ -1928,6 +1928,26 @@ exports.DataService = Montage.specialize(/** @lends DataService.prototype */ {
         }
     },
 
+    /**
+     * Resets an object to the last value in the snapshot.
+     * @method
+     * @argument {Object} object - The object who will be reset.
+     * @returns {external:Promise} - A promise fulfilled when the object has
+     * been mapped back to its last known state.
+     */
+    resetDataObject: {
+        value: function (object) {
+            var service = this._getChildServiceForObject(object),
+                promise;
+
+            if (service) {
+                promise = service.resetDataObject(object);
+            }
+
+            return promise;
+        }
+    },
+
     /**
      * Save changes made to a data object.
      *

data/service/raw-data-service.js

@@ -304,6 +304,24 @@ exports.RawDataService = DataService.specialize(/** @lends RawDataService.protot
         }
     },
 
+    /**
+     *
+     * Resets the object to its last known state.
+     *
+     * @method
+     * @argument {Object} object   - The object to reset.
+     * @returns {external:Promise} - A promise fulfilled when the object has
+     * been reset to its last known state.
+     *
+     */
+    resetDataObject: {
+        value: function (object) {
+            var snapshot = this.snapshotForObject(object),
+                result = this._mapRawDataToObject(snapshot, object);
+            return result || Promise.resolve(object);
+        }
+    },
+
     /**
      * Subclasses should override this method to save a data object when that
      * object's raw data would be useful to perform the save.