Update Vue.js, Quill and npm packages

TODO 1:

• Update Vue 2 -> Vue 3. See https://madewithvuejs.com/blog/vue-3-roundup
• Update Vuex 3 -> Vuex 4.
• Update Vue Router 3 -> Vue Router 4.
• Update vee-validate 2 -> vee-validate 4.
• Remove Vue-Quill-Editor and use VueQuill (or Quill for Vue3?).
• Update all other npm packages and reduce the number of npm packages.

• Update Go packages. See #124.
• What else?

TODO 2:

Pop-up messages are displayed with https://sweetalert2.github.io/ and with https://f3oall.github.io/awesome-notifications/. Only keep SweetAlert2 or Awesome Notifications.

Could they both be removed if one use Element+ instead of Bootstrap? https://element-plus.org/en-US/component/alert.html

TODO 3:

• Still use Quill but keep an eye on wangEditor, Tiptap and Jodit. Others ?

Rapido must be fast and easy to use. One must use the same languages (Stylus, TypeScript, Vue, Go...) in all packages, if possible.