Provide game object instead of just the board to players

[jbirkesteen]

Currently, the select_action() method for players take the board in matrix representation as an argument. This, however, leads to problems when we need to define the TDAgent (and, actually, also the minimax-agent, which currently re-use some code from connectFour to work around this).
The following needs to be done:

• [x] Re-write select_action() for all players
• [x] Re-write other methods of the Minimax-agent to rely on the definitions in connectFour (e.g., instead of its own place_piece().
• [x] Make sure that this change in use is reflected for methods calling select_action() (for instance in Env).
• [x] Write the remove_piece() method (from the minimax-agent) in connectFour, as both minimax and TD will need this.

This change should be fine, since the methods would usually be called from Env which has access to both players and connectFour.

[RasmusBrostroem]

Two minimax agents gives error in later stages of the game in place piece. Needs to be looked at more

[jbirkesteen]

Two minimax agents gives error in later stages of the game in place piece. Needs to be looked at more

The issue was that the initial value of the best_score did not depend on the loss_reward specified by the user, leading the player to choose column None when it couldn't avoid a loss. This was resolved in commit 88952cc.