Implement service worker offline page

Also, make sure it can be translated.

src/components/MigratingView.vue

@@ -0,0 +1,55 @@
+<template>
+  <div>
+    <transition name="slow-fade">
+      <div
+        class="text-center d-flex flex-column goodbye-wrapper"
+      >
+        <div class="quote">Migrating...</div>
+      </div>
+    </transition>
+
+  </div>
+</template>
+<script>
+
+export default {
+  name: "MigratingView",
+  data() {
+    return {
+    };
+  },
+};
+</script>
+
+<style lang="scss">
+  @use "@/assets/css/chat.scss" as *;
+  .author {
+    font-size: 80%;
+  }
+
+  .close {
+    position: absolute;
+    bottom: 40px;
+  }
+
+  .slow-fade-enter-active,
+  .slow-fade-leave-active {
+    transition: opacity 2.5s;
+  }
+  .slow-fade-enter, .slow-fade-leave-to /* .fade-leave-active below version 2.1.8 */ {
+    opacity: 0;
+  }
+  .goodbye-wrapper {
+    position: fixed;
+    top: 0;
+    left: 0;
+    bottom: 0;
+    right: 0;
+    z-index: 100;
+    color: black;
+    background-color: white;
+    align-items: center;
+    justify-content: center;
+    padding: 40px;
+  }
+</style>