Option to include notes in Export Mode

### Description

I would like to be able to export slides with my speaker notes included (that is, the contents of `` nodes for each slide).

### Proposal

One idea might be to provide anther query param, so the url would have `?exportMode=true¬es=true`. An alternative might be to configure this via a prop on ``.

I imagine the notes would be placed to one side of each slide, with a background which makes them distinct from the slide. (Perhaps the background could be configurable via a prop on `` itself?) I would suggest a fairly small default font size for these, so that more detailed notes can be included without taking up too much extra space.