🚸 ♻️ Refactor store and improve UX

- Move view related functions out of the store
- Restructure the store.js file
- Improve error handling of `/check`
- Show red loading spinner if data fetch failed
- Prefetch current, next and previous day instead of only current
- Refactor some other frontend file

src/App.vue

@@ -4,7 +4,7 @@ import TitleBar from "./components/titlebar-element.vue";
 import BottomNavbar from "./components/bottom-navbar.vue";
 import DateSelector from "./components/date-selector.vue";
 import LoadingElement from "./components/loading-element.vue";
-import { loading, loadingProgress, theme } from "./store";
+import { loading, loadingProgress, loadingFailed, theme } from "./store";
 import { computed, ref } from "vue";
 
 const autoThemes = { true: "dark", false: "light" };
@@ -31,7 +31,11 @@ const isDataView = computed(() => {
     :class="theme == 'auto' ? `theme-${autoTheme}` : `theme-${theme}`"
   >
     <TitleBar />
-    <LoadingElement :active="loading" :progress="loadingProgress" />
+    <LoadingElement
+      :active="loading"
+      :progress="loadingProgress"
+      :error="loadingFailed"
+    />
     <div class="center">
       <main>
         <DateSelector v-show="isDataView" />