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.
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
Merge branch 'master' into button
- 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.
Initial refactor of JDKPathConsolePanel.
Reason for this is to sync functionality between GUI and Console version
of the JDKPathPanel.
Cleanup of intial refactor of the JDKPathConsolePanel
Synchronizing JDKPathPanel with JDKPathPanelConsolePanel through
HDJPathPanelHelper
Console mode of JDKPathPanel should also skip if was set ot skip panel.
Actually check that path is valid when thinking of skipping the panel.
- Centralize error messages
- Centralize validation
- Fix bug where I was saving JAVA_HOME into the wrong variable key
Merge branch 'master' into IZPACK-1147
Ensure that on window's the program group contains valid syntax
Merge pull request #252 from mtjandra/IZPACK-1147

[IZPACK-1147] - Fixes for JDKPathPanel