added GameView class - it's the screen that has the board on it
added GameView class - the screen that has the board on it
- user enters a number between 1 and 9 in the box and presses enter to confirm
- if the input is invalid, the value is reset to null
- partially valid input such as "number5kfjSJ" will be reduced to "5". Similarly, "0005" will be reduced to "5". However, if there are any other numbers in the input such as in "15" or "50" the input will be considered invalid