Changes their endpoints and remove the user id from the URLs.
Simplifies list changes to share a single endpoint, which aligns it to
the behaviour of the existing sort preference endpoint.
Also added test to ensure user preferences are deleted on user delete.
- Primarily moved and re-organised view files.
- Included readme within views to document the convention.
- Fixed some issues with page field select list in previous commit.
- Tweaked some route names while going through.
- Split some views out further.
Closes#2805
