Some changes
 - App class moved to GUI package and renamed to Launcher
 - Warning policies changed : non javadoc documented members don't
trigger warning, but potentially non closed resources (such as file
reader / writer, etc.) trigger some
 - Serial added for exceptions and some other classes
 - AboutPanel moved in a simple JDialog instead of a JPanel in a
JLayeredPane in the WelcomePanel
 - LibraryDradAndDrop class created to handle drag and drop operations
in the card library. Not working yet
 - User object added in the image panel
 - Minor changes and bug fix
Menu enhanced, images added or modified, some more improvements