Bugfix: add pause image

Add the pause image in the assets/image folder.
Change asset of the drop and the sunscreen drop

- Better separate the frames in the spritesheet of the drop;
- Change the color of the sunscreen drop, because the previous color was
  similar to the spritesheet of the normal drop.
Fix the sound in the menu

Now the sound of the menu is correctly playing after we change to other
states of the game.
Bugfix: decrease two lives at once

Fix the bug of decreasing two lives at once when the player hits the hot
sand in normal state (drop is small).

Due to set the countCall variable to zero in the restartGame function, the
killDrop function is called twice. Hence, the life is decreased twice as
well. To overcome this problem, the countCall variable is now set to zero
in the create function.