Migrate to Vue 3 draft

[ordago]

This is a draft PR that deals with several of the chore parts of migrating a Vue 2 app to Vue 3 such as emits and changing lifecycle hook methods.
There are dependencies such as vue-js-toggle-button which are not compatible with Vue 3 that still need to be dealt with.

[igorski]

Hi @ordago many, many thanks for starting this initiative!

I had originally figured a move to Pinia was required as a prerequisite for updating Vue (which would complicate migration touching a sensitive part of the business logic), but I overlooked the fact that Vuex 4 still uses mutations.

My time is a bit more limited for the coming period but I'll be looking into the work you have done to get a clear idea of the total scope of the migration.