[Draft] Create numbered and bulleted lists

This PR aims to add the creation of lists in a document. This only aims to support numbered and bulleted lists and not image bullet lists for now.

# TODO
* [x] Editor UI buttons
* [x] Detect list style at selection
* [x] Ops for list insertion/removal
* [ ] OT support
* [ ] Convert selected text to a list or selected list back to text
* [ ] Default styles for numbered and bulleted lists

Use ``parentNode`` instead. ``parentElement`` doesn't exist in IE.