Implemented the FlatLaf 2.6 look and feel for the Scrabble game, by setting the game's UI to FlatLaf's FlatIntelliJLaf, rather than the default look and feel of a Java GUI. This new look and feel offers better looking JOptionPanes, JMenu and JMenuItems, JFileChoosers, rounded buttons, and hover animations for buttons (in this case, for the board's squares and tiles). The method that makes the UI change is called setScrabbleGameUI(). If there is an error in setting the Scrabble game's UI, the exception is handled and the Scrabble game's UI should remain unchanged and default to Java's generic look and feel.
Fixed a bug with the main menu of the game, where the game will not add player names to the player cards when 'Cancel' is clicked during the JOptionPane player name input prompt.
Updated calls to the JOptionPane in classes that do not have a reference to the JFrame by passing in JOptionPane.getRootFrame() method as the parent component, rather than passing in null. Providing a reference to the JFrame rather then passing null results in a centered JOptionPane (instead of a JOptionPane that is off to the side).
Also added a preferred width and height to the tiles to fix the issue of large/wide-looking tiles on each of the player's racks.