Updated ReversiAI

- Updated ReversiPlayer to no longer watch it's owned entities. This was
due to issues with copying the board. The board has new functions to
replace these.
- Updated ReversiBoard with several new functions for retrieving
entities and players, and cloning the board.
- Updated functions that used the ReversiPlayer to retrieve entities;
they now use the board. This removed at least one questionable
implementation, and improved others.
- Deprecated ReversiIntelligenceInputController.
- Created MinMaxAi to replace ReversiIntelligenceInputController.
MinMaxAi does not have recursion implemented yet.
- Separated functions of cloneBoard and cloneBoardPieces in Board class.
- Removed unused imports.