Variable name, declaration and assignment optimisations, Enum for directions and restart option.

[Abductcows]

I'd like to improve the readability of the project and add a restart button

Some examples for the readability part:

ranX= 0 + (int)(Math.random()*19); -> ranX = (int) (Math.random()*19)
directionSnake = 1 -> snakeDirection = Directions.RIGHT
ArrayList<ArrayList<DataOfSquare>> Squares= new ArrayList<ArrayList<DataOfSquare>>(); -> ... = new ArrayList<>();

[Abductcows]

#18 done, did not add the third part to maybe keep it compatible with older java versions