Merged PR 3: アプリ管理 page & some fix

![image.png](https://dev.azure.com/alicorn-dev/96136197-fa1c-44c2-b522-b9ab8b541f34/_apis/git/repositories/11e363ac-4aa8-4076-9a9a-eaac160866ff/pullRequests/3/attachments/image.png)

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Another commit is some refactoring and bugfix:

![prev.gif](https://dev.azure.com/alicorn-dev/96136197-fa1c-44c2-b522-b9ab8b541f34/_apis/git/repositories/11e363ac-4aa8-4076-9a9a-eaac160866ff/pullRequests/3/attachments/prev.gif)

frontend/src/layouts/MainLayout.vue

@@ -49,11 +49,18 @@ const essentialLinks: EssentialLinkProps[] = [
     link: '/',
     target: '_self'
   },
+  // {
+  //   title: 'フローエディター',
+  //   caption: 'イベントを設定する',
+  //   icon: 'account_tree',
+  //   link: '/#/FlowChart',
+  //   target: '_self'
+  // },
   {
-    title: 'フローエディター',
-    caption: 'イベントを設定する',
-    icon: 'account_tree',
-    link: '/#/FlowChart',
+    title: 'アプリ管理',
+    caption: 'アプリを管理する',
+    icon: 'widgets',
+    link: '/#/app',
     target: '_self'
   },
   // {