alerting: bad default state for notifiers

when we made image upload optional we didnt
show the default value properly in the UI. Which
caused confusing. This commit apply the default
values to existing notifiers in the edit pages
and reverts back to using uploadimage=true as the
default value.

public/app/features/alerting/notification_edit_ctrl.ts

@@ -43,6 +43,7 @@ export class AlertNotificationEditCtrl {
         return this.backendSrv.get(`/api/alert-notifications/${this.$routeParams.id}`).then(result => {
           this.navModel.breadcrumbs.push({ text: result.name });
           this.navModel.node = { text: result.name };
+          result.settings = _.defaults(result.settings, this.defaults.settings);
           return result;
         });
       })
@@ -89,7 +90,7 @@ export class AlertNotificationEditCtrl {
   }
 
   typeChanged() {
-    this.model.settings = {};
+    this.model.settings = _.defaults({}, this.defaults.settings);
     this.notifierTemplateId = this.getNotifierTemplateId(this.model.type);
   }