Add mustExist attribute to file fields.
Do not print 'null' during console installation if no label is defined
for a file field. This could easily come up when the user decides to use
    a description tag for their file field instead.
Updated xsd.
Fix for IZPACK-1009; update javadocs to have fewer missing piece of information.
RulesEngineImpl changed so that operands are not blindly added to the list of
operands for AndCondition / OrCondition / XorCondition. Instead, each condition
(and sub-condition) is checked for existence before being added; if any operand
in any expression doesn't exist, the whole expression will evaluate to false.
fix the complex expressions also
IZPACK-1109: align the warning messages to use the same language
- Ensure splash screen is only shown for GUI installations
- SplashScreen should only be shown if user has specified to use one in
  the guiprefs of their install.xml.
- New useSplashScreen modifier allows the user to specified minimum
  amount of time to display splash screen
- Notice that the splash screen must be displayed outside of the
  runnable, otherwise the splash screen will be grey
- Remove logic for adding splash screen to the Manifest
- Updating tests not the check for SplashScreen int MANIFEST.MF file
- Instead check that the "Spash.image" resource is available within the
  jar if it has been properly specified
Adding skeleton code to display a button through both console and gui
installations
Implementing skeleton to call button actions.
Remove redundant prompt method from the ConsoleField class. This prompt
method is handled by our Console class.
Use reflection to pass InstallData to the button action.
- Ensure to always use a GUIPrompt for GUI button events.
- Ensure to only print success message in console if user has selected
  to press button
Only try to load splash screen resource if defined in guiprefs.
Ensure that the buttons that control the custom panels adhere to its on
enabling rule when the custom field is enabled. Otherwise you will be
able to remove rows when there is only one row.
Hide buttons if minRow and maxRow are the same value. In this case there
are no need for row controls.
- Ensure that JAVA_HOME variable actually referes to the JAVA_HOME
  rather than the path to the java runtime environment
Allow autocompletion for specifying path to JAVA_HOME through console
installation.
[IZPACK-1146] GUI Installer - UserInputPanel radiobutton/checkbox variables set even though the panel hasn't been visited