Previously there was no spacing between the "Play all" and "Edit"
button in the playlist view. This fixes the issue by putting all
header buttons into their own "ui buttons" div similar to the
ArtistBase.vue component.

- use modals
- less proeminent button
- field styling/labels

Removes unnecessary `...` for more coherence

<dangerous-button> modal-confirm's slots.

SetInstanceModal.vue

Fix #612: Improved accessibility by using main/section/nav tags and aria-labels in most critical places

Fix #1