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

src/orm/model/events/ModelEvent.ts

@@ -0,0 +1,31 @@
+import {Model} from '../Model'
+import {Event} from '../../../event/Event'
+import {JSONState} from '../../../util'
+
+/**
+ * Base class for events that concern an instance of a model.
+ */
+export abstract class ModelEvent<T extends Model<T>> extends Event {
+    /**
+     * The instance of the model.
+     */
+    public instance!: T
+
+    constructor(
+        instance?: T,
+    ) {
+        super()
+        if ( instance ) {
+            this.instance = instance
+        }
+    }
+
+    // TODO implement serialization here
+    dehydrate(): Promise<JSONState> {
+        return Promise.resolve({})
+    }
+
+    rehydrate(/* state: JSONState */): void | Promise<void> {
+        return undefined
+    }
+}