Sprint 1: Implement & Test Placing Boats

[alinachiu]

Ensures that boats can be placed on the respective player's boat accordingly.

• Does not allow players to place boats on their opponent's board.
• Does not allow players not in the game to place boat pieces on either board.
• Does not allow players to place a boat piece in an already filled position

Note: does not check if the boat is valid; this check is done in the startGame function