Slides Style Settings

[Signynt]

Currently slides are always center justified, which looks pleasant most of the time, but when making slides with headings, especially multiple, it kind of looks weird imo.

## Heading 1
- Bullet 1
- Bullet 2
   - Bullet 3

### Heading 2
- Bullet 4

It'd be cool to have an option to change the justification, and perhaps also display the headings in different colors and sizes, like in a regular note.