add error handling

src/app/App.vue

@@ -9,6 +9,7 @@
         </div>
       </div>
     </div>
+    <ErrorBar/>
     <footer class="footer elevated">
       <Player />
     </footer>
@@ -27,12 +28,14 @@
   }
 </style>
 <script lang="ts">
+  import ErrorBar from "./ErrorBar.vue";
   import TopNav from "./TopNav.vue";
   import Sidebar from "./Sidebar.vue";
   import Player from "@/player/Player.vue";
 
   export default {
     components: {
+      ErrorBar,
       TopNav,
       Sidebar,
       Player,

src/app/ErrorBar.vue

@@ -0,0 +1,28 @@
+<template>
+  <b-alert
+    class="fixed-top m-0 rounded-0"
+    variant="danger"
+    :show="error != null"
+    dismissible
+    @dismissed="clearError">
+    <template v-if="error">
+      <strong>{{ error.message }}</strong><br>
+      {{ error.stack }}
+    </template>
+  </b-alert>
+</template>
+<script lang="ts">
+  import Vue from "vue";
+  import { mapState, mapMutations } from 'vuex';
+
+  export default Vue.extend({
+    computed: {
+      ...mapState(['error'])
+    },
+    methods: {
+      ...mapMutations([
+        'clearError'
+      ]),
+    },
+  });
+</script>