5 difficulty levels added for issue #96

[Xiaoxiaomingbao]

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• I have reviewed my submission thoroughly.
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✍ Description of the Pull Request

Please concisely describe the changes you have made.

• classes Difficulty.java and GameSettings.java added
• GreenDinoComponent.java and DinosaurMenu.java modified
• Modifications to other files are unnecessary

🔗 Issue link

Issue reference number and link goes here e.g. 'Fixes/Closes #96'.

• This Pull Request fixes the issue : 'Closes #'
• This Pull Request does not fix an issue.

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[github-actions]

👋 Hello @Xiaoxiaomingbao, thank you for submitting in Dinosaur Exploder 🦖 PR! To allow your work to be integrated as seamlessly as possible, we advise you to:

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[Xiaoxiaomingbao]

The user can choose a difficulty level at the start of the game.

As the difficulty increments, the dinosaur can move faster and send bullets in a wider range of angle.

[jvondermarck]

Awesome thank you !! Just resolve the conflicts, thanks !