Display Explicit Links with custom reference classes on Lepiter pages

[botwhytho]

Instances of LeAttachedLink show up in a pages 'explicit references' section but when one expands it, errors come up. An example that breaks is LeDatabaseReloadExamples>>#addAttachedLink.

Some links with external references, like with LeLinkExternalUrlReference just don't work. These types of links should show up in pages and their previews and spawned objects/tools should be different as they don't point to other pages. There should be machinery for users to create subclasses to link to and spawn arbitrary objects to Lepiter pages. Discord thread for more context.