Update sentence lists to lists of lists
Update sentence lists to be objects

Vue doesn't work well with arrays inside arrays, so the sentence lists
are wrapped in an object with a 'sentence' key.

TODO: fix grammar export
Update context menu grammar elements argument
Implement context menu update functionality
Update context menus
Add IDs to dummy grammar nodes
Refactor transforms to arrays with IDs
Update dummy grammar to use ID-based paths
Update interface to use new ID-based structure
Update context menu actions for new keypaths