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

What is the reasoning to go for literal description of these styles instead of generating them on the fly during construction, given that only 3 parameters seem to change which could be calculated?
For the latter I would see the advantage that the size of webodf.js would be smaller and it is easier to see how all styles relate to each other. Disadvantage would be runtime cost at startup. So what made you go for this solution?