Revert post status on failed save.

Refs #3667, Refs #3776
- If saving a post fails, revert its status back to the
  pre-save value.
- Added tests to check post status after failed save attempt
  on both new and existing posts.

ghost/admin/controllers/editor/new.js

@@ -11,9 +11,6 @@ var EditorNewController = Ember.ObjectController.extend(EditorControllerMixin, {
                 if (model.get('id')) {
                     self.transitionToRoute('editor.edit', model);
                 }
-            }).catch(function () {
-                // Publishing failed
-                self.set('status', 'draft');
             });
         }
     }

ghost/admin/mixins/editor-base-controller.js

@@ -211,6 +211,9 @@ var EditorControllerMixin = Ember.Mixin.create(MarkerManager, {
                 return model;
             }).catch(function (errors) {
                 self.showErrorNotification(prevStatus, self.get('status'), errors);
+
+                self.set('status', prevStatus);
+
                 return Ember.RSVP.reject(errors);
             });
         },