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

The main reason for this solution is that it would be easy to pull this out into an external JSON file for modification by consumers of webodf since that seemed like a good idea.

I hadn't actually considered calculating the styles using code but I think this approach is more readable and easier to understand. I did a quick check and this patch grows the gzipped webodf.js for me by about 3KB vs current master which I think is not too bad.