New model 2 grid size

As the user, I want to be able to set the grid dimensions manually, so I can get a different sized grid every time if I wish.

Conversation:

• At the start of the game the user needs to be prompted for the number of grid rows and columns.
• Doing so can change the difficulty of the game, as a bigger grid makes it harder to guess where the opponent's ship is.
• If the user chooses to restart the game, they need to be prompted again for the grid size.

Confirmation:

• There needs to be a visible option to enter the number of rows and columns at the beginning of the game.
• When we hit 'restart', there should be another prompt for the grid size.