Migrate to use Pinia over Vuex

Does this PR close any open issues?

Depends #334

Give a longer description of what this PR addresses and why it's needed

This vastly simplifies the store object that we have to maintain. We've gone from requiring mutations, to not, and we now have a path forward on the vue 3 sanctioned store library. While this change wasn't strictly necessary for that change, we're now not using direct-vuex, and we no longer need to use computed get/set logic to update. That is a huge simplification.

I made this an extension of #334 so that we can have these improvements on top of the vite changes.

The only remaining changes to get us fully up to date with vue 3 will be migrating to it, and using vuetify 3. Vuetify is still in beta, and not well documented at the moment. I think it would be prescient to wait a little while longer for that migration.

I removed some javascript Set logic here, since vue 2 doesn't deal with the reactivity of Sets. We can plan to add that back when we're using vue 3, since they are supported there.

Provide pictures/videos of the behavior before and after these changes (optional)

There should be no change

Are there any additional TODOs before this PR is ready to go?

TODOs:

[x] Update relevant documentation
[x] Make issue to upgrade to vue 3 and vuetify 3
[x] Make issue to use Sets for unique arrays
[x] Make a fix for the multinet-components LoginMenu component
[x] Make issue to convert the store to setup store (a step towards #137)

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multinet-app / multilink