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

src/event/Event.ts

@@ -0,0 +1,11 @@
+import {Dispatchable} from './types'
+import {JSONState} from '../util'
+
+/**
+ * Abstract class representing an event that may be fired.
+ */
+export abstract class Event implements Dispatchable {
+    abstract dehydrate(): Promise<JSONState>
+
+    abstract rehydrate(state: JSONState): void | Promise<void>
+}