Figure out an upgrade path for Vue 3

[robbevp]

In february Vue 3 (actually vue 3.2) will become the new default. So I guess it's about time we start thinking about this upgrade.

Since Vue 3 also chnages/switches some of the tooling around vue. As outlined in the blog post:

• vuex is switched to pinia
• vue cli switched to vite
  Neither of these are easily upgradeable without switching to Vue 3. (I tried swapping the cli for vite a while ago, but couldn't get it to work)

The upgrade won't be easy because of a few things:

• There are some problems with memory leaks in vuex as noticed in Memory leak when commiting tracks music-quiz#25
• Pinia doesn't have mutations as vuex did. However, having tight control over this is important to keep memory usage reasonable
• Vuetify is still working on their upgrade

Maybe we might be better starting from a blank slate and then move the views/components/logic into the new app? That might be easier to figure out than trying to upgrade everything at once

[chvp]

Vuetify 3 has data tables these days, which seemed to me like the major blocker for upgrading to vue 3. Switching to pinia should be possible without switching to vue 3 (it was done in dodona-edu/dolos#759), so should probably be done separately to avoid the PRs becoming even bigger than necessary.