Add basic concepts for event bus, and implement in request and model

src/orm/model/events/ModelUpdatedEvent.ts

@@ -0,0 +1,9 @@
+import {Model} from '../Model'
+import {ModelEvent} from './ModelEvent'
+
+/**
+ * Event fired right after a model's data is updated.
+ */
+export class ModelUpdatedEvent<T extends Model<T>> extends ModelEvent<T> {
+
+}