feat: Add slick code styling

[matthew-carroll]

Description

Flutter and Dart developers want to show Flutter and Dart code. It's important that the code styling experience be top notch.

slick_slides already has great code styling. Port that approach to flutter_deck.

Requirements

• [ ] Add dependency on syntax_highlight
• [ ] Integrate with existing code display
• [ ] Look for places to take the existing code display to a higher level with that package