Use keyed each blocks

[Slartibartfass2]

Currently, we don't use keys for svelte each blocks. According to the docs, this is good because svelte can then diff the elements and reload the items correctly.
There's an ESLint rule for that: https://sveltejs.github.io/eslint-plugin-svelte/rules/require-each-key/
We should investigate why the rule doesn't apply and enforce this behavior.