Improve Table of Contents macro functionality in new editor

When editing a page with the new editor, I have to add the TOC element last. Anything else and the page corrupts very easily.

The TOC element also causes two further issues:

1. Because it's invisible you can't change any of its settings in the Template editor. You literally can't do anything with a template after you've added a TOC it without risking corruption but as we have a couple of tweaks to the ToC this is just a little cherry on top.

2. The style and way the ToC is drawn has changed its position for the worse. It's clearly different from the legacy editor.