feat: Upgrade editor (#1227)

* WIP

* document migration

* fix: Handle clashing keyboard events

* fix: convert getSummary

* fix: parseDocumentIds

* lint

* fix: Remove unused plugin

* Move editor version to header
Add editor version check for API endpoints

* fix: Editor update auto-reload
Bump RME

* test

* bump rme

* Remove slate flow types, improve themeing, bump rme

* bump rme

* fix: parseDocumentIds returning duplicate ID's, improved regression tests

* test

* fix: Missing code styles

* lint

* chore: Upgrade v2 migration to use AST

* Bump RME

* Update welcome doc

* add highlight to keyboard shortcuts ref

* theming improvements

* fix: Code comments show as headings, closes #1255

* loop

* fix: TOC highlighting

* lint

* add: Automated backup of docs before migration

* Update embeds to new format

* fix: React warning

* bump to final editor version 10.0.0

* test

README.md

@@ -109,7 +109,7 @@ Outline is composed of separate backend and frontend application which are both
 
 Outline's frontend is a React application compiled with [Webpack](https://webpack.js.org/). It uses [Mobx](https://mobx.js.org/) for state management and [Styled Components](https://www.styled-components.com/) for component styles. Unless global, state logic and styles are always co-located with React components together with their subcomponents to make the component tree easier to manage.
 
-The editor itself is built ontop of [Slate](https://github.com/ianstormtaylor/slate) and hosted in a separate repository to encourage reuse: [rich-markdown-editor](https://github.com/outline/rich-markdown-editor)
+The editor itself is built on [Prosemirror](https://github.com/prosemirror) and hosted in a separate repository to encourage reuse: [rich-markdown-editor](https://github.com/outline/rich-markdown-editor)
 
 - `app/` - Frontend React application
 - `app/scenes` - Full page views