Add toggle to switch the theme (light/dark)

[FrancescoCoding]

Description

It would be cool to enhance the software with a dark theme and a button to toggle between light/dark.

Implementation Requirements:

Core:

• Have a toggle to switch between the themes

Should:

• Save user preference to config.json file
• Logic should be implemented in its own directory, not in main.rs

Could:

• Have a minimum border radius and a square look to maintain the Minecraft-like theme