I can see the intent, sadly this was always broken in the case where the
post already has a custom thumbnail from initial load, and we don't drag
any new files. It did not actually remove the existing thumbnail.
Before 12c4542bb2482fac89aae9a04b15984a56bb8fb0 it would actually crash,
but this now makes it behave as expected.
Also properly syncs internal state with what's displayed to the user.
Print all links through new uri.js component
Refactor the router to use more predictable parsing
Fix linking to entities with weird names (that contain slashes, + etc.)
