Allow setting display style for bricks

- [ ] Allow the user to configure available display styles for each brick
- [ ] When display styles are available, show them as a dropdown for the brick
- [ ] When no display style is available, don't show the dropdown
- [ ] Extend Brick model/table to hava a display_style field (string)
- [ ] Provide instructions in readme on how to configure display_styles for an application
- [ ] Provide instructions in readme on how to use display_styles
- [ ] Add changelog entry