Introduce a concept of "non-urgent" toasts

This is somewhat expected to be temporary.

src/stores/NonUrgentToastStore.ts

@@ -0,0 +1,50 @@
+/*
+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.
+*/
+
+import EventEmitter from "events";
+import { ComponentClass } from "../@types/common";
+import { UPDATE_EVENT } from "./AsyncStore";
+
+export type ToastReference = symbol;
+
+export default class NonUrgentToastStore extends EventEmitter {
+    private static _instance: NonUrgentToastStore;
+
+    private toasts = new Map<ToastReference, ComponentClass>();
+
+    public static get instance(): NonUrgentToastStore {
+        if (!NonUrgentToastStore._instance) {
+            NonUrgentToastStore._instance = new NonUrgentToastStore();
+        }
+        return NonUrgentToastStore._instance;
+    }
+
+    public get components(): ComponentClass[] {
+        return Array.from(this.toasts.values());
+    }
+
+    public addToast(c: ComponentClass): ToastReference {
+        const ref: ToastReference = Symbol();
+        this.toasts.set(ref, c);
+        this.emit(UPDATE_EVENT);
+        return ref;
+    }
+
+    public removeToast(ref: ToastReference) {
+        this.toasts.delete(ref);
+        this.emit(UPDATE_EVENT);
+    }
+}

src/stores/ToastStore.ts

@@ -15,9 +15,10 @@ limitations under the License.
 */
 
 import EventEmitter from "events";
-import React, {JSXElementConstructor} from "react";
+import React from "react";
+import { ComponentClass } from "../@types/common";
 
-export interface IToast<C extends keyof JSX.IntrinsicElements | JSXElementConstructor<any>> {
+export interface IToast<C extends ComponentClass> {
     key: string;
     // higher priority number will be shown on top of lower priority
     priority: number;
@@ -55,7 +56,7 @@ export default class ToastStore extends EventEmitter {
      *
      * @param {object} newToast The new toast
      */
-    addOrReplaceToast<C extends keyof JSX.IntrinsicElements | JSXElementConstructor<any>>(newToast: IToast<C>) {
+    addOrReplaceToast<C extends ComponentClass>(newToast: IToast<C>) {
         const oldIndex = this.toasts.findIndex(t => t.key === newToast.key);
         if (oldIndex === -1) {
             let newIndex = this.toasts.length;