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
Merge pull request #246 from Shrafe/IZPACK-1109

Izpack 1109
Merge pull request #247 from mtjandra/IZPACK-1442

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