- 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
Merge pull request #247 from mtjandra/IZPACK-1442

[IZPACK-1442] - Ensure not to display splash screen on console and automatic installations