[Vue] Add loading skeletons for about page

aleksis/core/assets/components/about/InstalledAppsList.vue

@@ -4,6 +4,14 @@
   >
     <template v-slot="{ result: { error, data }, isLoading }">
       <v-row>
+        <v-col v-if="isLoading" v-for="idx in 3" cols="12" md="6" lg="6" xl="4" class="d-flex align-stretch">
+          <v-card class="d-flex flex-column flex-grow-1 pa-4">
+            <v-skeleton-loader
+                type="heading, actions, text@5"
+            ></v-skeleton-loader>
+          </v-card>
+        </v-col>
+
         <InstalledAppCard
             v-for="app in data.installedApps"
             :key="app.name"