Add Exit and Difficulty Selection Functionality to Side Panel

[theblackethiopiandude]

Issue Description

Our Java Swing Minesweeper game lacks essential functionalities: graceful game exit and difficulty selection. Let's enhance user experience by adding these features.

Exit Functionality

Implement an "Exit" button for players to gracefully exit the game, improving user satisfaction and adhering to software standards.

Difficulty Selection Screen

Introduce a screen/dialog for players to choose difficulty levels (Beginner, Intermediate, Expert) before starting a new game. This empowers users to tailor their gaming experience.

Proposed Implementation

1. Exit Button: Prominently position an "Exit" button in the game interface for easy access. Clicking it should gracefully close the game window.

2. Difficulty Selection Screen: Implement a screen/dialog for users to select difficulty levels before starting a new game. Ensure clear instructions and visually distinct options.

3. Integration: Seamlessly integrate these features into the existing codebase for smooth transition between game states.

Expected Benefits

1. Improved User Experience: Easy game exit enhances user satisfaction. Difficulty selection offers tailored challenges.

2. Customizable Gameplay: Players can adjust the game's difficulty to match their skill level.

3. Enhanced Accessibility: Clear exit options and difficulty selection cater to diverse player preferences.