Refactor / clean up the javascript

Problem/Motivation

There is a number of issues with the js.

E.g.
📌 Pointless code: Drupal.node_edit_protection = {} RTBC
🐛 Pointless code: The "all links and buttons" part has no effect Needs review
🐛 Use once() and context to prevent accumulated event listeners Needs review
🐛 Pointless code: String return value from onbeforeunload Needs work

Steps to reproduce

Proposed resolution

It will be easier to handle them in a big PR.

Remaining tasks

User interface changes

API changes

Data model changes