fixed a typo in a comment
added a method to the get the player object that identifies the opponen of the current player object
moved a method from "ConnectFourGame" to board as it is not depending on a current game configuration - just the board
added a comment to the method opponent
(re)added a method to specify/identify illegal masks
added a method to get the next moves, but those that are particular important (killer moves) first ;refactoring to reduce the amount of code