Correct assertion in HumanPlayer test

Check for the correct thing, that a move was
made on the specified position with the right
mark.
Replace magic numbers with meaningful constants in ComputerPlayer
Remove unnecessary code and test from ComputerPlayer

Mark field not needed since Board provides the
the mark that goes next. Test was removed since
it was slowing down the suite for no good reason
since the behaviour is covered in other tests.
Correct index for making a move on the Board

This places the responsibility of getting the correct
move on the CliDisplay instead so the calculation is
made there.
Make ComputerPlayer constants private
Increase encapsulation and readability of core classes

- Change getGrid() to private
- Add getValueInPosition() as alternative for testing
- Replace numbers and strings with constants
- Make constants private
Add method in PlayerFactory to return description for all game choices
Remove duplication from CliDisplay

Using PlayerFactory to validate a game choice
Remove board choices duplication from CliDisplay

Board now provides the map with choices and values
and any client can use that instead.
Fix Board choice message for CliDisplay