Break out actions and payloads to their own files

The definitions take up a lot of space which makes it hard to see the dispatcher class, so break them out.

src/dispatcher/actions.ts

@@ -0,0 +1,23 @@
+/*
+Copyright 2020 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Dispatcher actions also extend into any arbitrary string, so support that.
+export type DispatcherAction = Action | string;
+
+export enum Action {
+    // TODO: Populate with actual actions
+}
+