Create Task (Gaurish and Athena): set different levels to the game

[Athena9355]

• [ ] set different difficulty levels
• [ ] allow the user to pick the level of difficulty before each game
• [ ] the different levels will differ in: speed of the ball, chances of the AI missing a hit
• [ ] higher points will be awarded to harder levels (e.g. scoring a point in a easier level will +1, but scoring a point in a harder level will +10 etc.)