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
* [x] OT support
* [x] Convert selected text to a list or selected list back to text
* [x] Add feature flags and session constraints
* [x] Default styles for numbered and bulleted lists

Automatically assigning (as in: setting) might be too much for existing lists (that might break the intention of the original creator of the list). Just using it when rendering would be good, yes (but perhaps you meant this).

But I was also thinking about properties which are not set, so some built-in default values would be used. That needs to be defined somewhere as well. At least by how I understand the schema currently that can happen. Hm. Need to think more about that.