Refactor layout components and add loading state

- Refactor the layout components to improve code organization and readability.
- Add a new store called LoadingStore to manage the loading state.
- Update AppLayout.vue, AppMenu.vue, AppTopbar.vue, ScenarioStore.js, and UserPrefStore.js to import and use the LoadingStore.
- Add loading indicators in AppTopbar.vue and ScenarioList.vue components.

src/layout/AppLayout.vue

@@ -64,6 +64,7 @@ const isOutsideClicked = (event) => {
     <div v-if="userPrefStore.userLoaded" class="layout-wrapper" :class="containerClass">
         <app-topbar :page="page"></app-topbar>
        <div class="layout-sidebar">
+
             <app-sidebar></app-sidebar>
         </div>
         <div class="layout-main-container">