Board, pieces and hex_side_length adjusted to device screen, added background image

CheckersClient/android/assets/Game/1x/StarBackground1x.png

...kersClient/core/src/com/mygdx/game/UniCheckersClient.java

...t/core/src/com/mygdx/game/controllers/GameController.java

CheckersClient/core/src/com/mygdx/game/model/Game.kt

...rsClient/core/src/com/mygdx/game/views/CinematicView.java

CheckersClient/core/src/com/mygdx/game/views/Constants.java

CheckersClient/core/src/com/mygdx/game/views/PlayView.java

...lient/core/src/com/mygdx/game/views/tokens/StarPiece.java