Add concept of imported resources to editor

[piemonkey]

Overview

This is covers 2 parts of the 3-part story of snippet rdfa linking:

1. Snippet creation: Defining 'placeholder' resource URIs that will exist in the final document, making them accessible to the RDFa tools when creating a snippet and allowing us to create links from those resources to nodes in the snippet. Links to those resources is more troublesome and will come in a later PR.
2. Template creation: Mapping placeholder resource URIs to real resource URIs that exist in the document.

The UI for linking placeholder resources to real ones is very rough, but should work for now.

connected issues and PRs:

Plugins PR: lblod/ember-rdfa-editor-lblod-plugins#462
and RB PR: lblod/frontend-reglementaire-bijlage#263.

Setup

Needs to be tested by being used in the plugins repo.

How to test/reproduce

See plugins PR for test steps.

Challenges/uncertainties

There were some problems with types after converting a component to gts and adding the necessary types packages. I think these were just being hidden by being assigned to any, so I had to convert some template only components to use gts to correct these.

Checks PR readiness

• UI: works on smaller screen sizes
• UI: feedback for any loading/error states
• Check cancel/go-back flows
• Check database state correct when deleting/updating (especially regarding relationships)
• changelog
• npm lint
• no new deprecations

[piemonkey]

Reviewed as part of lblod/frontend-reglementaire-bijlage#263 so merging this.