Read comments... Update: JavaDoc, etc.

Please add javadoc for (some variables or anonymous class comments are
missing):
1. setInitialStates() in SettingsPanel
2. MenusPanel constructor
3. menusActionListeners(), keyBindings(), menuPanelActionListeners(),
levelsPanelActionListeners(), instructions(), settingsActionListeners()
and scoresActionListener() in MenuFrames (just add comments about the
anonymous classes).
4. LevelsPanel constructor
5. fileExists() in HighscorePanel
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