Templated Minimax

[andreimesquita]

Depends on Negamax for Tic-Tac-Toe.

Create a generic implementation of the Negamax algorithm to be used in almost any game.
Use template and polymorphism to generalize the actual code used by the Tic-Tac-Toe game.

Generalize existent methods:
- getScore(state : state_type) : int
- getState(board : board_type) : state_type

Create the following methods:
- isLeaf(state : state_type) : bool
- getNextBoards(board : board_type) : std::vector<board_type>