CheckerBoard.Java
- moved jumpAvailable to Square.java
- if a square has a jump it is set to true in findValidMovesForSquare

Square.java
- Removed int[] validMoves because it was redundant
- Added member function printValidMoves that prints to the logcat with
valid move position numbers and tells if the square has a jump available
- renamed nextSquares and its gettter and setter to validMoves
- added getters and setter for jumpavailable

CheckersActivity.java
- cleaned up the valid move printing with Square.printValidMoves