Improve UX for adding new fields from the page

[Stvad]

Right now it's quite cumbersome. Some things that I think can improve the experience:

• Merge add view into the display view
  • Basically allow people to click a plus button in the bottom and add an arbitrary field (repeatedly)
  • Do the on-the-page entities discovery fully async
• Allow connecting entities that are not found from the page (via direct id entry, and via search)
• Don't push the buttons out of screen view (esp when there is enough space)
• (current add view) Add a signifier that indicates that it's possible to change the field type you're adding

Issues to fix:

• If none of the links resolve to anything the add view is forever stuck in the "waiting" state