Webapp: Migration to `vue 3`

[Rotzbua]

Many preparations and migrations have already been completed (see #649).
Still outstanding is the migration of vuelidate #899, which should be done before.

Reasons for migration

• vue 2 reached end of life: 31 Dec 2023

Problems

• local library copy of qrcode.vue must be updated
• huge dependency on UI library vuetify
• vuetify has a lot of incompatible API and layout changes
• vuetify some components are missing

Almost no migrations are necessary with regard to vue 3. The big problem is vuetify. vuetify requires a lot of work,maybe choose other UI framework like https://quasar.dev/ .

Migration

Migration: https://v3-migration.vuejs.org/
Breaking changes: https://v3-migration.vuejs.org/breaking-changes/

• update initialization
• model binding

[peterthomassen]

See #699 for some partial work on this.

[peterthomassen]

@Rotzbua Would you like to take another stab at this?