Autocomplete while typing links to other pages

[irskep]

Method A:

1. Include a list of all page slugs in a JS constant
2. Port slugify to JS
3. Write a custom CodeMirror plugin which shows a list of matches and picks one when you press Enter

Method B:

1. Write a JSON endpoint to return a list of page slug matches for a given string
2. Write a custom CodeMirror plugin which shows a list of matches and picks one when you press Enter